Manchester City manager Pep Guardiola could be without defenders Ruben Dias and Nathan Ake for Sunday's Premier League showdown with rivals Manchester United.
Both players started in the 2-0 FA Cup fifth-round win against Peterborough United on Tuesday night; however, the pair were replaced at half time by Aymeric Laporte and John Stones.
Guardiola has since revealed that Dias and Ake were forced off due to injury and their availability for the Manchester derby is now in doubt.
Speaking in his post-match interview, Guardiola said: "Nathan finished bad in the action when he got the yellow card [at the end of the first half] and Ruben was not feeling good in his leg.
"That's why, for caution and to be alert, we made the substitutions. It was not planned but Aymeric and John were excellent [in the] second half. I would say it was a medical decision."
Both players will now face a race against time to be fit for the 4.30pm kickoff time at the Etihad Stadium.
Dias would be the most likely candidate to start on Sunday, as opposed to Ake, with Laporte seemingly favoured at centre-back ahead of Stones, who has recently been competing with Kyle Walker for a place at right-back.
Academy graduate Cole Palmer is City's only other injury concern, with the midfielder missing over a month with an unspecified problem. body check tags ::
