Manchester United captain Wayne Rooney has suffered a knee ligament injury that could rule him out for up to two months, according to reports.
Rooney was missing from the travelling squad United announced on Wednesday morning for Thursday's Europa League last-32 first-leg clash at FC Midtjylland.
In the squad announcement on United's official website, the club said boss Louis van Gaal was "expected to confirm why his captain has not made the trip during his pre-match press conference at 1700 GMT".
A number of national newspapers subsequently reported the 30-year-old striker had sustained knee ligament damage that could sideline him for two months.
United, meanwhile, maintained they would be making no further comment on the matter until Van Gaal's press conference.
If Rooney is facing such a period on the sidelines, it will be a significant blow both to his club and country.
United are currently fifth in the Barclays Premier League, six points adrift of fourth-placed Manchester City with 12 rounds of top-flight fixtures to go.
And Van Gaal, whose position has been under increasing scrutiny, admitted after Saturday's 2-1 loss at Sunderland that winning the Europa League was looking the most viable route into the Champions League for his side.
Meanwhile, England have a double-header of international friendlies next month against Germany and Holland as they continue their preparations for this summer's Euro 2016 finals.
Three Lions head coach Roy Hodgson said on Saturday that skipper Rooney - England's all-time record goalscorer - will be ''a player we need to depend upon'' at the tournament in France.
Rooney has netted three times in four appearances for England this season, and is United's top scorer this term with 14 goals in all competitions.