Tom Cleverley is a doubt for Manchester United's trip to neighbours and Premier League title rivals Manchester City on Sunday.
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England midfielder Cleverley limped out of United's 1-0 defeat to CFR Cluj in the Champions League just before half-time on Wednesday night with a calf problem and was replaced by Paul Scholes.
After the match at Old Trafford, which United went into with their status as Group H winners already assured, manager Sir Alex Ferguson admitted he was concerned about the 23-year-old's condition ahead of the trip to the Etihad Stadium.
"We will assess Tom in the morning." Ferguson said. "He felt his calf a little but it is not good news. We'll see what he's like tomorrow."
Ferguson had already said that central defender Nemanja Vidic is unlikely to make his long-awaiting comeback in the derby. The United captain is set to fully return to the first-team picture next week.
However, Ferguson believes Shinji Kagawa has an outside chance of featuring this weekend following the Japanese playmaker's absence with a knee injury sustained at the end of October, though he is also more likely to be available again next week.
"Shinji is now back and is doing some running," Ferguson said. "I don't know if he'll make Sunday's game. It might be a bit early for him.
"At least he's back training and he'll hopefully join in the football part next Monday."
United make the short journey across town with a three-point lead over the champions at the top of the table.