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Manchester City captain Vincent Kompany's return to action has been delayed due to toxins in the Belgian defender's blood, with manager Pep Guardiola saying the Sky Blues have to be "careful" with his fitness.

The Spanish manager confirmed that Kompany is back in training and performing well, but he revealed that caution is being taken over getting him back in the starting lineup ahead of Tuesday's UEFA Champions League clash with Borussia Monchengladbach, per Mark Ogden in The Independent:

It's a doctor issue. He has something in his muscle and we believe that was a problem for the many injuries last season. He's getting better, but he has a little bit toxic (in his blood). That's why you have to be a little careful. I think it's the last part of that because he is training with the group. When I see him, I say, this guy can play, because he's training like Vincent is. But the doctor said, with what happened in the past, we have to be careful.

Kompany, 30, has been out of action since May with groin and thigh problems and missed the UEFA Euro 2016 tournament after undergoing surgery.

He endured a frustrating 2015-16 campaign as numerous fitness concerns restricted him to only 13 Premier League starts, per WhoScored.com.

Guardiola has excellent cover at his disposal for the Belgian. Alongside John Stones, Nicolas Otamendi was particularly superb in central defence as City beat Manchester United at Old Trafford on Saturday, per the Manchester Evening News' Stuart Brennan:



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However, City still miss Kompany's leadership and need him back in action as soon as possible as they look to fight for silverware on several fronts this term.

Outside of Otamendi and Stones, Aleksandar Kolarov and Bacary Sagna are both able to play as makeshift centre-backs, but neither is a natural in the position.

Meanwhile, Eliaquim Mangala has been sent out on loan to Valencia following two disappointing seasons at the Etihad Stadium after his 2014 move from Porto for £32 million.

Kompany's return to the starting XI could be crucial in the long-run for City this season as they look to win the Premier League again.

It is unsurprising, though, that City are being cautious with the former Anderlecht man given his injury history.

They should have few problems seeing off Gladbach without their skipper—especially as City will be boosted by their Manchester derby win.

But Guardiola will likely be eager to give Kompany some minutes in upcoming Premier League clashes against Bournemouth and Swansea City before October 2's tough visit to Tottenham Hotspur.