Wayne Rooney will miss Manchester United's Europa League game at FC Midtjylland on Thursday, the English football giants said in a statement on Wednesday.
England striker Rooney, the United captain, was not in manager Louis van Gaal's 18-man squad which travelled to Denmark on Wednesday for the last-32 tie.
"Wayne Rooney is a notable absentee from the flight and the manager is expected to confirm why his captain has not made the trip during his pre-match press conference at 1700 GMT," said a statement on United's website.
Defender Matteo Darmian also missed out on the trip to Denmark after dislocating his shoulder during the 2-1 Premier League away to Sunderland last weekend.
Adnan Januzaj is cup-tied, having played in the competition earlier this season while on loan at Borussia Dortmund.
United's loss to Sunderland left them fifth in England's top flight and six points off a top-four finish -- the club's "minimum requirement" in Van Gaal's words — that would secure entry into next season's Champions League.
Defeat in Denmark would merely add to the pressure on van Gaal, with speculation mounting that former Chelsea manager Jose Mourinho is set to replace the beleaguered Dutchman at the end of the current season.