Manchester City will be without Kevin De Bruyne for Wednesday's trip at Old Trafford.
The midfielder limped out of City's 1-0 win over Tottenham Hotspur in the Premier League on Saturday and Pep Guardiola has ruled him out of the derby.
De Bruyne has suffered an injury-hit campaign and this is the third time he's picked up a problem that has forced him to miss a period of action, with the Belgian starting just 11 Premier League games this term.
Asked for an update on De Bruyne's fitness, Guardiola said: "It's a muscular problem, we'll see in the next days if he's getting better but for tomorrow he's not available."
De Bruyne has twice picked up knee injuries this term and since then he's struggled with the occasional muscle problem.
Guardiola believes the relentless schedule in England has played a part in that and while he hopes the 27-year-old will be back before the end of the season, he will focus on restoring him to full fitness for the start of next season.
"It was one injury then another and another, now he's had two or three muscular problems since his knee. Normally with the competition in England they have to take the physical condition playing games, now we have to pay more attention to the little details," Guardiola said.
"We have to see if he can play one or two more games before the end of the season. He has a lovely family, his life is incredibly well organised with training and rest.
"We'll speak with him, the doctors and the physio's for him to be fit."
Man City star Raheem Sterling's anti-racism manifesto is brilliant - but he shouldn't have to do it
