THE highlight of Gerhard Tremmel’s career was his League Cup win with Swansea City in 2013 but had history panned out differently, it might just as easily have come under the lights at Celtic Park. And, perhaps, if we stretch the notion a little further it might even have extended to this Tuesday evening.

Tremmel, an amicable Bavarian with an understated laugh, will have a foot in both camps when Celtic host Bayern Munich in midweek as they seek redemption from their 3-0 humbling in the Allianz Arena a fortnight earlier.

The former goalkeeper served such as Hannover 96, Hertha Berlin, and Energie Cottbus with distinction in his homeland before a season at Red Bull Salzburg ended with him pitching up at Swansea City’s 2011 pre-season training camp in Austria, hoping to secure a move to the Premier League.

The man who gave him his big break in England’s top flight was none other than Brendan Rodgers, who offered him a deal after Tremmel impressed during a 45-minute spell in a pre-season friendly against the Glasgow side. Celtic, then managed by Neil Lennon, were similarly impressed and also approached Tremmel about signing in the aftermath of the fixture.

Tremmel, a man of his word, had already promised Rodgers that he would sign for Swansea, so declined Celtic’s offer. He might just have changed the course of history had he opted to make the move to Parkhead. Fraser Forster was in between loan spells from Newcastle United and Celtic were weighing up their options.

“I was out of contract and I had a trial at Salzburg and Brendan said he wanted to see me in a pre-season match. Celtic were looking for a goalkeeper and weren’t sure whether they could keep Fraser Forster. Brendan told me in the office that he wanted to sign me and after that the Celtic goalkeeping coach [Stevie Woods] said you should think about signing for us and you could be our long-term No 1.”

Tremmel admits that as a result he has a soft spot for the club. It was one of life’s sliding-doors moments. At 38, an age when plenty of goalkeepers remain active, it’s not beyond the realms of possibility to suggest that Tremmel might have been lining up against Bayern. He says he would have relished the chance.

“Celtic are special. I always liked Celtic. If they had approached me sooner, I would have signed for them for sure. I always had that mental picture in my head of playing in front of that amazing crowd. Playing in an Old Firm game. I simply would have loved that. I’d love to see them and Rangers in the Premier League.”

Following the end of his playing career Tremmel returned to his native Munich, where he now serves as Swansea’s assistant head of European recruiting. He spent a year during his youth career at the city’s second club, 1860 Munich, and had an even longer period as a kid at Bayern. As someone who spent intermittent spells as a No 1 and a No 2 goalkeeper, he empathises with Sven Ulreich, the incumbent at Bayern, following the foot injury to Manuel Neuer that will keep the best goalkeeper in the world on the treatment table until January. He is doubly sympathetic since Ulreich’s agent also happens to be one of Tremmel’s best friends. “When you get the opportunity to go to Bayern Munich you have to take the chance even if you know Manuel Neuer is the best, or one of the best, goalkeepers in the world. You have to go and try it because to play for Bayern Munich as No 1 only comes once in your life.

“I think he did well to get there. Bayern win a lot of games and Manuel Neuer is very consistent but this is exactly what you have to work for; when the No 1 gets injured you have to be on top of your game.

“You can always learn from the other goalkeeper. He might do things a little bit different and you might think, ‘I might try that’. But when you are playing against so many good players than you would in a mid-table or lower-league team, that ultimately improves you. At Bayern Munich you have to win every game. It is a special situation when you are the No 1 of a really big club because you are maybe only facing two shots on target in a game. If you don’t improve then you are doing something wrong.

“I believe there are two different types of second goalkeeper, those who are determined to break in and become No 1 and those who are sitting comfortably in the No 2 spot. I was always desperate to play. I gave my everything in training, tried to impress the manager even though you know the chance you are going to play is very, very small. It was not my nature to accept sitting on the bench. Football is about playing, at the end of the day.”

The solitary existence of the goalkeeper is an oft-debated facet of football. Playing in the position demands a mental strength that none of the other members of a team require – there is a need to develop a Teflon coating as quickly as possible. Ulreich, a long-time starter at Stuttgart and a German Under-21 international, sacrificed a guaranteed starting role and the right to be judged objectively, when he agreed to become Neuer’s deputy in 2015. Last month, Ulreich felt the sting that comes when expectation turns to anger. With his side leading 2-0 at home to Wolfsburg, the 29-year-old flapped at a free-kick and allowed the visitors a lifeline which they duly accepted, before forcing an equaliser seven minutes from time. However, if there was one area of the Bayern Munich backline that Celtic might have hoped to exploit, Tremmel does not believe it will lie in the hands of Ulreich. A month on from that howler, the goalkeeper has steadied his nerves.

“I think it is a mental thing. When you know Manuel Neuer is out injured you know you have the chance to play every week, that puts a little bit of pressure in your mind straight away. You want to do as well as possible obviously. You want to impress. You have waited for the chance, now you want to show everybody how good you are. It’s part of the human reaction.

“You should take it as a chance and just play but you’ve got to see it as a player. He’s probably sitting in a hotel thinking, ‘OK, I’m now playing for the next two or three months’ and when these things pop in your mind they are not good. You have to play loose.

“The media will talk negatively. They’ll say ‘Oh, my God, Manuel Neuer is injured. Can the second goalkeeper play in the Champions League?’. They put a lot of doubt into his head. But he is a very experienced goalkeeper and he is working hard in training. There have been a couple of mistakes, but he has made a lot of good saves which no-one has really focused on. But he has kept his feet on the ground and he has got his reward.

“I know where he [his mental state] is and he’s very calm. When he made the mistake against Wolfsburg it got into his mind a little about the free-kick but if he just keeps calm he will be fine because he has all the ability. I never had any doubt that he could do it because he is a good goalkeeper and the atmosphere at Celtic Park will be good for him.”

Tremmel says Jupp Heynckes has already made a difference at Bayern and he believes Celtic will have it all to do on Tuesday night. “From what I saw in Munich it was not good for Celtic. Brendan Rodgers likes brave players and his players were not brave in that game. He likes his players to want the ball and they have to play football. They had no confidence at one point and Bayern were giving them a going over. It came down to a lack of quality. I think Brendan knows that.”