Manchester United playmaker Shinji Kagawa has been ruled out for up to a month with a knee injury.
The Japan international was substituted at half-time during Manchester United's 3-2 victory over Braga in the Champions League on Tuesday night.
And United boss Sir Alex Ferguson has confirmed Kagawa will be out for up to four weeks with an injury similar to the one which kept Ashley Young on the sidelines.
"It's a similar injury to the one Ashley Young had," Ferguson said on Goal.com. "He's going to be out for three to four weeks. Playing on with the injury didn't help the situation for him."
The former-Borussia Dortmund midfielder has made solid start to his Old Trafford career, hitting a couple of early goals before tailing off in recent weeks.
Kagawa has found himself struggling to establish a place in a team including Wayne Rooney, Robin Van Persie and either Javier Hernandez or Danny Welbeck, and most of his appearances so far have come in the left midfield position.
The Japanese star now looks set for a prolonged spell on the treatment table, and faces a race against time to get fit for the first Manchester derby of the season on December 9.
United currently trail Premier League leaders Chelsea by four points going into their crunch fixture this Sunday, but a victory would see that lead cut down to just a single point.
Manchester United's last visit to Stamford Bridge ended 3-3, and another goal-fest could be on the cards when the two meet this weekend.
Sir Alex Ferguson's side have been slow starters this season, and again fell behind on Tuesday night. Portuguese side Braga opened up a 2-0 at Old Trafford before United eventually overhauled them to win 3-2.