Manchester United's misery at their Champions League exit at the hands of Basel on Wednesday was compounded by an injury to defender Nemanja Vidic.
The Serb was stretched off with a knee injury after a clash with Basel striker Marco Streller before half-time.
"We don't know with Vidic," manager Sir Alex Ferguson told reporters. "It's certainly a medial ligament but hopefully that's the worst it is."
Vidic looks set for an extended spell on the sidelines having also missed the opening weeks of the season for United, who have been plagued by injuries recently.