James Forrest is out of Celtic's tie with AC Milan tomorrow at the San Siro.
The winger was already carrying an injury but has now been ruled out through illness.
Tonight Manchester United may have to face Bayer Leverkusen without Danny Welbeck and Phil Jones, Wellbeck has a knee injury while Jones has an ankle injury.
Wayne Rooney is expected to start and will once again wear his protective head gear.
In tonight's other action Viktoria Plzen host Manchester City in the Czech Republic.