Manchester United goalkeeper David de Gea missed last night's match with FC Midtjylland after sustaining an injury in the pre-match warm up.
He now faces a race to get fit for their upcoming fixtures - and his potential absence could have an impact on the title race.
Manager Louis van Gaal told The BBC after the game: "David de Gea has a knee problem so we have to wait and see. We will investigate that with a scan."
United are likely to select deputy Sergio Romero for the upcoming FA Cup clash with Shrewsbury Town on Monday, with squad rotation likely anyway.
Then, De Gea faces a race to be fit for the match with Arsenal at Old Trafford in the Premier League the following Sunday.
United have already lost captain Wayne Rooney to injury sustained last week against Sunderland, and the De Gea injury is a big boost to Arsenal's chances of winning the fixture.
The tie should have been a tricky one for the Gunners, sandwiched between their Champions League matches with Barcelona, but the prospect of a weakened and out of form United lessens the chances they will drop points and cede the initiative to their title rivals.