league campaign on 17 August after picking up a virus.
The 22-year-old contracted a virus on United's pre-season in Nigeria and has not trained since.
"I doubt Wayne will be fit for the start of the season" said United boss Sir Alex Ferguson.
"It's a virus he picked up in Nigeria and it's not a nice one. He's not been back in training yet."
Ferguson revealed Rooney's illness was diagnosed by the club's own laboratory.
Sir Alex will have a dilemma in the opening match of the season at home to Newcastle, because of Rooney's illness and Ronaldo's injury.
Portuguese midfielder Nani is suspended while Anderson is on Olympic duty with Brazil.
As it stands, Ferguson has only Carlos Tevez, untested youngster Fraizer Campbell and Louis Saha to choose from up front.
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