Manchester United defender Chris Smalling could be sidelined for up to three months with glandular fever.
The heavy cold which kept the 22-year-old out of the Boxing Day win against Wigan Athletic is feared to be worse than expected, according to the Daily Mail.
Smalling moved to Old Trafford from Fulham in summer 2010 for around £10m.
Rio Ferdinand and Phil Jones are both expected to return to action for Saturday's match at home to Blackburn Rovers following minor knocks.