Manchester United interim manager Ralf Rangnick rejected any suggestion that there was more to Cristiano Ronaldo's absence from his team for Sunday's 4-1 defeat to Manchester City than a hip injury.

Former United captain Roy Keane had questioned how genuine the injury was during the Sky Sports broadcast of the derby, saying: "We talk about Ronaldo being some sort of machine, he's very rarely injured and then every now and again he comes out... and says hip flexor. It doesn’t add up to me."

Keane made similar comments after the game and Rangnick was asked in his news conference to respond.

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“The doctor came to see me on Friday and told me Cristiano cannot train due to a problem with his hip flexor and the same was true on Saturday and that’s why he couldn’t be part of the squad,” Rangnick said.

“It’s just a fact if players tell the medical department that they are injured and they cannot play I have to accept it," he added.

United were also without their Uruguayan forward Edinson Cavani due to injury but Rangnick said he had been fit enough to train.

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"Edi trained in the last three days, he trained well but he still felt after those three training sessions yesterday afternoon that he is still not fit to play. This is a fact. As a manager, I cannot force a player if he does not feel fit enough or well enough to play," said the German.

United have slipped out of the top four after their loss and Arsenal's 3-2 win over Watford left them a point behind the Gunners having played three games more and Rangnick said there was little room for error.

“I didn’t actually expect Arsenal to lose at Watford so for us it’s clear, if we still want to have a chance to finish fourth at the end of the season, we can almost not drop any more points," he said.