Danish club FC Copenhagen will miss Ghana striker Razak Pimpong for Tuesday's Uefa Champions League clash with Benfica.
The 23-year-old, who is suffering from a severe flu, has been left out of the squad for the match in the Portuguese capital Lisbon.
Pimpong contracted the flu on his return from international duty in London last week, where the Black Stars drew 1-1 with Australia.
"I had this terrible flu since I returned from the Australia game and this has kept me away from training," Pimpong told BBC Sport.
"It is a shame that I could not travel for the game Lisbon but I hope to return to training by next week."
Manchester United lead the group with nine points from four matches ahead of Celtic on six, while Copenhagen and Benfica trail on four points each.