The cliché goes that the hardest thing for a professional athlete to do is to walk away from the sport they love. It’s why Cristiano Ronaldo is grimacing and gesticulating his way around Germany right now attempting – and so far, failing - to defy biology at the age of 39, and why countless boxers fight on long past their peak to the detriment of their health. It wasn’t that way for Charlie Mulgrew, though.

When the former Celtic, Aberdeen, Dundee United and Scotland defender took the decision to hang up his boots last September, he did so knowing that he had taken every blow from football that he could possibly handle. And a few more besides.

The incessant, crushing pressure. The debilitating knot in the stomach before matches. Feeling as though he was ‘playing with a 50-kilo backpack on – and looking like it’, as he puts it, during those final dark days at United.

Mulgrew might come across as one of the most laidback men imaginable, but make no mistake, it was all getting to him. He recognises now that he fell into that trap that so many footballers do, hiding their fears and anxieties behind a thin veneer of machismo. Finally, he had had enough.

Now, as he takes his first steps into coaching with Hamilton Academical’s under-18 side, he is hoping that his experiences at the top level of the game can help the young players under his charge navigate its pitfalls better than he was able to.

On a personal level, the role has given him back his love of the game, which he is now more than happy to watch from the sidelines.

“I don’t miss playing,” Mulgrew said.

“Not once have I looked at the games since I retired in September, genuinely, and wished I was playing. I play sixes twice a week, and that’s great, I enjoy that.

“I sometimes miss training and being in the changing room, but the pressure games were bringing me was outweighing my motivation for actually playing.

“Listen, being a football player is huge pressure. It’s not spoken about enough. There is so much fear and anxiety involved in playing in front of that crowd. You live your life in a glass bowl, you are constantly judged. It’s difficult. It’s something you need to deal with and learn to live with, but I don’t miss that side of it.

“I feel now a lot more equipped to probably deal with that side of it. If I go back to maybe my 17-year-old or 18-year-old self and give myself the mindset I have now, I’d probably be a lot more equipped to deal with it.

“But now, I’ve got a strong passion for going into the coaching and management side, and I want to pass that experience, that knowledge and emotional intelligence onto players, and let them understand that I know what they are going through, and let them go and play with freedom within a structure and how I see the game.”

Now and again, a player will touch upon the thorny subject of their mental health, but it is usually couched in a defiant riff about how they thrive under the pressure that football brings down upon them. Or they might joke about a teammate who is sick before matches.

“I was never a spewer,” Mulgrew said.

“If I’m spewing, I’m steaming! But I’m telling you, it’s not spoken about enough.

“I’ll tell you what the tell-tale sign is. See in the winter, you wake up in a hotel for an away game. Someone tells you, and this has happened to every football player, that the game is off.

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“In the pre-match meal, the atmosphere goes from nobody saying a word to through the roof, because all of a sudden there is a weight off your shoulder and the place is buzzing. It’s like, ‘wow’.”

Handling that pressure – or at least, appearing to - is a prerequisite for any player, particularly, in a Scottish context, when representing Celtic or Rangers, as Mulgrew has. And despite the impact it had on him, he wouldn’t have swapped it for the world.

“That’s the thing, you still want to be there,” he said.

“This is the crazy thing about it. You live your life and that is your passion. You want to be at the top end of it, playing for Celtic and these teams that want to win.

“It comes at a cost, but it’s the greatest thing ever when you win. So, when you win, amazing. But there is a lot of fear and pressure that goes into that.

“You live your life with everybody judging you, and if you lose, it is a nightmare until the next game, then you can win and relax again.

“Did I used to panic before games? Of course. If you aren’t nervous before a game, there is something wrong with you. It’s human nature.

“You go out in front of 60,000 fans who are demanding that you win and that are scrutinising every single thing you do. But it’s why you are a Celtic player, and why when you win you get that buzz, and when you don’t, you get that other side of it.

“Any football player I know…well, it doesn’t get spoken about enough in football, but it’s hard.

“What I’m saying is that there is a lot of fear, but there is nowhere else you would rather be, that is true, because you wouldn’t. But that doesn’t mean that it’s not hard. Anything worth having in life, it’s hard, but it’s still amazing.

“For example, getting beat off Rangers to lose the league on the last day is a complete low, and it is horrendous. You’ve had all the nerves and the fear in the build-up and that has happened.

“To then win the double in the season there when Adam Idah scored in the last minute in the cup final, those are the highs that you live for, and there are a lot of them at Celtic.”

That paradox is something that has been on Mulgrew’s mind a lot since his own son, 16-year-old Joshua, went full-time at Celtic last month.

When a manager of Celtic and Rangers signs a player, they will talk of wanting to attract the right sort of character as much as they discuss a footballer’s ability, but while Mulgrew will be lending as much of his own experience as he can to his offspring, he knows there is nothing that can really prepare him for what lies ahead.

“It’s hard,” he said.

“You just don’t know, you don’t have a crystal ball.

“My wee boy has now gone full time with Celtic, and people ask me if he has got a chance. Can you get inside his head? Because I don’t know what he’s thinking. I know what I was thinking. I know I had a lot of doubts and fears and a lot of resilience, and if I could give any young boy anything, it would be resilience.

“Can you go through the lows? Because there will be plenty of them. Some of them are really low. Some of them are as little as getting dropped from the 18s team or the 21s. You could be training with the first team, have a nightmare, and then the next day you aren’t training with them.

“There are so many lows, and it is about how you can bounce back from them.

“You could be released from Celtic like me, then you go to Wolves, then you get released from there. You then go to Aberdeen, don’t miss a game, play well and get back to Celtic.

“So then, all of a sudden you’re thinking, ‘hold on a minute, how am I back here?’ “It’s just mad, and I suppose that is life as well. It is who can get up from the downs, and that is resilience for me.”

What happens though when all you have are the downs? Alas, that is how Mulgrew’s professional career ended, as the highs that once compensated for everything else that came with being a footballer dissipated at Dundee United.

He was accused of not caring by some of the Tannadice faithful as the club spiralled towards relegation, of downing tools in their hour of need. But he wants to set the record straight. He was willing, but both his mind and his body, ultimately, were not.

“That was horrendous,” he said.

“My last year at Dundee United was…it was always going to take a season like that to see me out.

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“The season before, we finished fourth and got into Europe, and the only highs in that season were winning 1-0 and scrapping through the game.

“A lot of the games, you didn’t really enjoy, but you won, and you could go, ‘yes, we can drive down the road and we’ve won’.

“We finished fourth, got into Europe, and I didn’t enjoy it, but we won games and we were in Europe so I thought I’d continue playing.

“Then we win 1-0 [against AZ], and we are buzzing, then we go away and lose seven, and from there on it was just a downwards spiral.

“I didn’t play against Celtic, but to lose nine, you were just spiralling into depression then. The fear and everything is coming, and then you are just getting beat, getting beat and getting beat.

“Before you know it you are on the pitch and you are lower than a snake’s belly confidence-wise, and you get accused of downing tools.

“The last thing you want to do as a human being is down tools, but you are gone. You are emotionally drained, you have no confidence, you are bordering on depression. But the fans are judging you, saying you are downing tools and booing you every time you get the ball.

“You’re in front of 12,000 fans who are accusing you of not fighting for the club. Of course you are, every single thing you are doing behind the scenes is to get this club to stay in the league, because who does it benefit for the club to go down? It doesn’t benefit me.

“I want to end on a high and stay up, but you are almost playing with a 50-kilo backpack on mentally, and that is how it looks.

“You end up trying too hard, you’re overthinking it, everything.”

Mulgrew had reached the point he had once dreaded – the end of the road. But all he found there was an overwhelming sense of relief.

“That was it,” he said.

“I still took time to think about it, because I had an offer from [Partick] Thistle and an offer from Hamilton, and I told the managers the same thing, that I didn’t know if I had the motivation that was going to outweigh everything else.

“Before a game, if I’m running out at Stirling Albion - no disrespect to Stirling Albion - I’m getting the same pressures. Even though you’ve played in the Champions League, you still want to win and don’t want to make a fool of yourself. You still have all these pressures.

“But then, does the benefit outweigh that feeling? And in the end, it didn’t for me.

“I sit here now and if I regretted it, I would say to you that I had made a bad decision. And I probably would have gone [back] into the game within a few months, because I’m still fit, but I have never once missed it.

“It’s given me a huge motivation though to have a group of players that I can understand how they are feeling, and we can address that and say you know what? There’s nothing you can do about it.

“It’s there and there is no getting away from it, but for me as a leader I just want to see you playing football the way you did in the school playground and go and play with freedom.

“I can watch my team and they know that is the main thing.”