In a challenging match against Borussia Dortmund, Celtic goalkeeper Kasper Schmeichel appeared to struggle, raising concerns about his performance and fitness as he navigates the later stages of his career.

Former Manchester City teammate Richard Dunne expressed his worries, suggesting that Schmeichel must remain vigilant to avoid the pitfalls of aging as a professional athlete.

The match, which ended in a staggering 7-1 defeat for Celtic at Signal Iduna Park, was a tough outing for the veteran keeper.

Despite his extensive experience, Schmeichel found himself under relentless pressure from a formidable Dortmund side, and while he made several attempts to keep the scoreline respectable, it was a night where few players in green and white could claim to have performed well.

Dunne, who retired in 2015 aged 36,  noted that while Schmeichel's struggles were evident, it would be unfair to place the blame solely on him.

The entire Celtic squad faced a steep learning curve against a team that has proven itself at the highest levels of European football.

This defeat served as a stark reminder to Brendan Rodgers and his team that they must significantly improve if they hope to compete with the elite clubs, particularly those like Dortmund who have recently reached the UEFA Champions League final.

That's despite Celtic continuing to dominate domestically, topping the Scottish Premiership with maximum points as it stands.

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"Kasper has been amazing," Dunne told Virgin Media Sport while on  punditry duties for the Spain vs Denmark UEFA Nations League match this weekend.

“He’s had a fantastic career, and he’s played in some really big clubs. He’s won the Premier League, he’s won an FA Cup, he’s played in the Champions League, and now he’s come and found himself playing for Celtic to come in to replace Joe Hart.

“I think at 37 you need to be very careful. You need to keep that mobility and that agility and what Kasper has always done when he’s been in goal, he’s been reactive to saves. 

“He’s really sharp on his line. And just going back to the Dortmund game that we watched a few weeks ago he wasn’t the sort of Kasper Schmeichel that we’ve been we’ve seen in previous years.

“He looked a little bit sluggish. Wasn’t as quick getting down to certain things and I think in the moment you look at it and you think are they huge mistakes or not? Probably not. 

“But then the more you analyse it, and you get closer into it and look at it deeper, sometimes his position is not right. He’s not reading the shot correctly. He’s not reacting. 

“Obviously when you get older, you’re not as conditioned as you used to be. You can’t train as hard as you used to.

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“And Kasper’s had a really good season. He’s done really well in the league. When you go and play in the Champions League it’s a level up, obviously, playing against Spain is a level up, and you’re playing against against better strikers and that. 

“And he just looked a little bit sluggish, a little bit rusty. He didn’t look as sharp as he should be. He’s normally a player who, when he has the ball at his feet, you can trust but he was taking chances as were the whole Celtic team. 

“I mean, it’s a different story with Denmark where they have a defence who’s organised, who’s structured, who defend deep.

“In that one game, Celtic weren’t great defensively. They were really poor and normally Kasper will get them out of a lot of trouble. 

“And just on that evening, he didn’t and that’s why I just think at 37 years of age, you need to be at your sharpest, you need to try hard and you need to make sure everything’s perfect and he just didn’t look bang on it that night.”