Owen Hargreaves is expected to be sidelined for another five weeks following his latest injury setback.
The Manchester United and England midfielder started his first game since September 2008 on Saturday, but limped off against Wolves after only five minutes with a hamstring injury.
United manager Sir Alex Ferguson today revealed Hargreaves, who has struggled with knee problems for two years, will be out of action until the middle of next month.
"We were at the stage where we knew Owen's knee was okay," said Ferguson. "His training performances for eight or nine days previously had been terrific.
"He had done really well, which is why we took the chance. But maybe the tension in the build-up was too much and he suffered because of it."
In addition to tomorrow's derby meeting with Manchester City, the 29-year-old will miss United's remaining two Champions League group games as well as their Carling Cup quarter-final against West Ham at Upton Park.
Ryan Giggs is also ruled out of the City game, while Nani has a groin injury and is a serious doubt for the Eastlands clash.
United's problems are not made any easier by a virus that has swept their training ground, with Patrice Evra, Nemanja Vidic, Dimitar Berbatov and Paul Scholes all believed to be among the victims.
Meanwhile, City manager Roberto Mancini has defended £24million striker Mario Balotelli after his red card at West Brom on Sunday.
"Mario is a young guy, a top player, sometimes he can make a mistake. That is normal," Mancini said. "The punishment was too severe."
