Manchester United interim manager Ralf Rangnick defended his medical team after Roy Keane questioned Cristiano Ronaldo's absence for Sunday's crushing 4-1 derby defeat to Manchester City.

Reports late on Saturday suggested Ronaldo would not feature at the Etihad Stadium on Sunday, with Rangnick confirming before kick-off that the Portugal forward was suffering from a hip problem.

United were also without Edinson Cavani, who was missing for a sixth consecutive game due to injury as they fell to a humiliating loss at neighbours City.

Former United captain Keane, speaking on Sky Sports before the game, suggested Ronaldo's omission may be down to other reasons after being left out for such an important fixture.

Keane insisted the decision did not "add up", with Rangnick citing a hip flexor problem that kept the forward out of training on Friday, and the German responded to the comments after the match.

"I have to believe my medical department," Rangnick told reporters when asked about Keane's thoughts on the Ronaldo situation.

"Our doctor came to see me Friday morning before training and told me that Cristiano could not train because of some problems with his hip flexor and the same was true on Saturday and that's why he couldn't be a part of the squad."

Rangnick appeared frustrated to be without Cavani once more ahead of the clash with Pep Guardiola's side, suggesting the Uruguay international ruled himself out of contention.

After the game, the former RB Leipzig boss again commented on Cavani being ruled out of the derby, insisting he could not make a player feature if they did not feel fit enough.

"What does it help if I tell you it is frustrating? It is just a fact. If players tell the doctor and the medical department they are injured and cannot play, I have to accept it," he added.

"I cannot force a player to play if he's not available because of an injury."

Pressed for an answer on whether Cavani decides when he is available, Rangnick responded: "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.

"We have to be – and I am – happy with the players we have. This is clear. We lost two, if not three strikers since Christmas, everybody knows.

"But this is a fact and we have to deal with it. I am not complaining about that."

The defeat at local rivals City leaves United a point adrift of fourth-placed Arsenal, who were 3-2 victors at Watford earlier in the day and have played three games fewer.

But Rangnick wants to focus on his team's push in the Champions League and hunt for a place in England's top four in the coming weeks, despite continued questions over who will take over at Old Trafford when his short-term contract concludes.

"Look, I'm still the manager of this team for another 10 games in the Premier League and hopefully a few more games in the Champions League," he continued.

"It doesn't make sense now to start speculation about how many players would we need and in what positions, this is my issue.

"Right now it's about preparing the team for the Tottenham game and after that, for a very important game against Atletico [Madrid] in the Champions League."