CELTIC have gradually taken a shine to football's ugly duckling.

The Europa League is the Champions League's unloved stepson but Uefa's lesser competition has been increasingly satisfying for the Parkhead club. The most glamorous fixture of their six-game group campaign will take place in Glasgow tonight and, even with a 6pm kick-off sapping the atmosphere and reducing the attendance, there will be a little stardust on show from visitors Atletico Madrid.

Celtic's participation in the Europa League has been unlike any other campaign by a Scottish club in Europe, ever. From the start it was suggested that they could do without the demands of still being involved when their priority was to win the Clydesdale Bank Premier League. Sion's expulsion from the tournament for fielding ineligible players against them in the qualifying round, and Celtic's readmission, left them with six additional fixtures which some felt they could do without. In addition, having been beaten 3-1 by the Swiss over two legs, it was claimed that Celtic had little to look forward to beyond another half-a-dozen bad results.

Not so. The European ties have not only kindled their growing affection for the Europa League itself, they have acted as a major catalyst for their improved domestic form. After a predictable defeat in Spain they drew at home to Udinese, which would have been satisfactory enough were it not for the fact Ki Sung-Yueng put them ahead with an early penalty and the Italians fielded a weakened team. But when they came up against what has proved to be the weakest team in the group, Rennes, Celtic found their feet and began to really play. They drew 1-1 in France, then beat them 3-1 in a highly rewarding Parkhead tie at the beginning of this month.

It looked like the same old story when Rennes scored early, but suddenly Anthony Stokes buried the ball in their net twice in the space of 13 minutes before Gary Hooper added a third. Celtic had a precious win which they followed with others against Motherwell, Inverness Caledonian Thistle, Dunfermline Athletic and St Mirren.

"The players haven't looked back from that Rennes game," said manager Neil Lennon. "It gave them a real shot in the arm, winning against such class opposition off the back of getting a good point away from home."

Two months ago it seemed as though Celtic went into midweek Europa League ties with one eye anxiously on the subsequent league fixture, lest they lose any more ground to Rangers. They are at Dundee United in four days' time, yet tonight the focus is entirely on Atletico Madrid.

"Sunday is an important game. We could be going into that seven points behind again so we have to be wary of it. But I think the Atletico game is an occasion we have been waiting for for a while. We have real top-class European opposition coming here. Our players have progressed as the group has gone on. They have become more confident about competing at that level. This is the fifth game in this group so they have had a good look at some quality teams. They know the step they have to take now. It's the type of game I want them to experience. The players want to play against Atletico Madrid. Who wouldn't? I would love to be playing in the game myself. I am not getting complacent and I know the players know they haven't cracked anything yet. This is a totally different concept, a different game, and I think we'll need a different approach."

Atletico Madrid have yet to win an away game in either La Liga or the Europa League this season (they drew 1-1 in Rennes and lost 2-0 in Udine) but they are top of Group I on goal difference. In playmaker Diego and Colombian striker Radamel Falcao, signed from Porto for £35m and ready to return after a hamstring injury kept him out for two weeks, they have players of genuine international class. Diego and Falcao scored the goals in the September tie.

Atletico took the lead against Real Madrid in the Bernabeu on Saturday night, only to lose 4-1. Their record in that fixture is awful and Real ultras taunted them with a banner saying "wanted: some worthy opponents for a decent derby". That will not mislead Lennon. Celtic supporters will tonight see the best side to play at Parkhead so far this season.

A few of the regulars inevitably will miss the game because of Uefa's insistence on a 6pm kick-off. "I don't think the early kick-offs help with an atmosphere," said Lennon. "That's probably the only disappointing aspect going into this game: it might not be a full house; 6pm makes it difficult for people to get away from their work, make it through the traffic and get here in time. With a bumper game like Atletico Madrid, given the quality and the flair they are going to play with, it's a shame the game is so early."