Pep Guardiola is facing a battle to keep Nicolas Otamendi happy at Manchester City – and accepts the club may lose the Argentine centre back.

Otamendi was one of the key figures in City’s Premier League title triumph last season, but has been a peripheral figure this term.

The 30-year-old, who was dubbed ‘Superman’ by Guardiola, is now seen as a back-up to first choice pairing John Stones and Aymeric Laporte.

City’s manager admits Otamendi is unhappy with his situation – but is unwilling to offer him any assurances of more regular first team football.

“He's not happy,” said Guardiola. “I don't have an answer. When he plays he's happy, when he doesn't play he's not happy, but not just Otamendi, everybody. All of them.

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“I don't know what I can do. Be honest with myself and with them, for sure. I am.

“We would like to (keep him), but it depends on the players and the agents.”

Otamendi has made just eight Premier League starts this season. Guardiola accepts that at the peak of his career he is unlikely to be prepared to play a bit-part role, but has told any unhappy players they are free to leave this month.

“I don't want sad players here,” he said. “I said now, during the transfer window, if you are not happy you knock on Txiki Begiristain's door.

“We need to be enthusiastic and happy to be here and at the end of the season they have to reflect on that.

“If maybe they don't play, when it doesn't happen they have to move, they have to leave. The only way to have success is to be happy in what you are doing.

“I know they are able to do it and I don't have any complaints about that."

While Stones and Laporte have developed one of the most effective central defensive partnerships in Europe, Guardiola insists he still has faith in Otamendi.

"He's a guy who plays with problems, with kicks, with muscular issues and always he's there,” he added. “It's incredible. What I said last season remains the same for me, it doesn't matter if he plays more regularly than last season.

“Aymeric can help us in the build-up on the left side. He's playing at a top, top level and I've got three central defenders and Vinny (Kompany) as well, but Vinny has problems quite regularly.

“When he played Southampton and Liverpool, Vinny was excellent, but we have John and Nico.

“John came back good after the World Cup, started really well and I want to give him confidence because he's a young player. He doesn't have the routine to play a lot of games like Nico.

“In the end with Nico, I know we can count on him at any time in any situation because he's an incredible professional and always he's ready.

“I'm delighted with him but I can understand him (wanting to play more). I cannot say anything else.”