JOHN BROWN would take a glance to his side and know there and then whether he was in for a game or not. At Hampden next month, the same theory will apply for Rangers.

In the red hot atmosphere of Old Firm battle, Brown has seen players freeze. When the spotlight has shone on them, experienced professionals have taken stage fright and failed to perform.

It is a situation Mark Warburton will hope doesn’t strike those he entrusts with a Light Blue jersey when they line up against Celtic. With a Scottish Cup final spot at stake, Rangers need to stand up and be counted when the action gets underway.

There have been European encounters where Brown took his first strides onto the park knowing that Rangers were already ahead. He knew who was up for it, and who wasn’t.

The build-up to the derby duel will be nothing like Warburton or his players have experienced before but they have to be ready to go even before the first whistle sounds.

“Oh yeah [I’ve seen guys freeze],” Brown said. “You can see it in the tunnel. You will check out your opponent’s eyes and see who is up for the game. It is a cup game and a chance to get to the last game of the season, which is always the best. If you are in the cup final and you win it, you have a great summer. If you are knocked out in the final, it is a hell of a five, six weeks before you come back. Both teams know it would be a great end to the season and both teams might have won the league.

“I think the Leeds United game [was won in the tunnel], but not against Celtic that I can remember. There were certain European games where the opposition froze in the tunnel. It was something Graeme Souness always said. Look into their eyes and if they can’t stare you back then you are 1-0 up.

“In the Old Firm games, there weren’t many in the tunnel because both teams, at my time, were mainly British players and the foreigners came in later on. The British players knew the intensity that the game was going to have. We never won many in the tunnel then. We had to do it on the park.”

The semi-final showdown will be a step into the unknown for Warburton and many of his players. They will have read about it and heard about it, but won’t know what the Old Firm rivalry really means until they live it for themselves.

His first taste of derby day was an occasion that even took Brown by surprise, and he knows the experience of those who have been there and done it will be crucial for the Gers.

“It was just a 5-1 victory,” Bomber said as he recalled his debut in August 1988. “Ray Wilkins scored, but we went one down to a goal from Frank McAvennie. Rangers had a good, solid side then. I was a bag of nerves before the game, but you get that - if you don’t have the butterflies there’s something wrong but once you’re over the line there’s not a bigger game in the country than the Old Firm. Adrenaline gets you through.

“You maybe don’t enjoy the 90 minutes - you just want to get a result - and then enjoy it afterwards. A lot of players have never experienced that and neither has Mark Warburton.

“He’s going into the game and will rely a lot on the experience of Davie Weir and he also has players such as Kenny Miller and Lee Wallace in the camp, good pros, who will keep the other players right.”

With Rangers’ promotion to the Premiership set to be confirmed sooner rather than later, Warburton will have four Old Firm clashes to look forward to next term. The Gers booked their place in the semi-finals with a convincing win over Dundee on Saturday and they will head to Hampden in fine form and high spirits.

“Every Rangers fan will be looking to win the league next year, although the directors will probably say it’s a bit early,” Brown said. “The team has improved since the St Johnstone game, they have learned, they’re no longer being hit on the counter attack. Dundee are a good side and were taken apart at the weekend but it’s a tougher task against Celtic.

“They are going through some hard times just now but they’re still clear at the top of the league and they’ve got the chance to do the same and do a double to win the Scottish Cup. It’s a massive game but there’s no pressure on Rangers.

“Saturday’s game would have given the manager another indicator as to the strength of his squad, playing against a solid Dundee side that have been doing very well in the Premiership. The Celtic game will give him a big bearing on how far the team has come on and that will dictate what he needs for next season.”

*John Brown and Chris Sutton were speaking at a media event to promote the new launch of the Glasgow Royal Hospital for Children.

The Glasgow Children’s Hospital Charity - the new name for Yorkhill Children’s Charity - is a charity close to John and Chris.

It raises money to support the 160,000 boys and girls from around Scotland who are treated at the hospital every year.