Park Ji-Sung is facing another two weeks on the sidelines with a troublesome knee injury he picked up on international duty.
The 28-year-old played in South Korea's 2-0 win over Senegal in Seoul a fortnight ago but having come through the game unscathed found his knee swelled up on the flight home.
The injury has kept the winger sidelined ever since and Manchester United Sir Alex Ferguson admits medical staff our mystified as to what the problem is.
The former PSV ace has missed the Red Devils last eight matches last turning out for the champions in the 4-3 win over neighbours Manchester City last month.
"We are having a little issue with Ji-Sung Park at the moment. His fitness has been poor since he came back from Korea," Ferguson said.
"He had no problem with the game but travelling back has given him a swollen knee which we don't quite understand so there are some issues with that.
"He could be out for a couple more weeks yet which is a blow."