Wayne Rooney has a chance of making the bench for United's title-decider at Wigan on Sunday.
The striker has been struggling with a hip injury, sustained in the draw at Blackburn last month, for the past few weeks and has missed the Reds' last two games.
Sir Alex will wait and see how the striker is over the next 48 hours, but believes a substitute's role is the best he can hope for.
"He may be on the bench," Sir Alex told reporters at his pre-match press conference. "He'll certainly be fit for the Champions League final."
The United boss also confirmed he is hopeful of having Nemanja Vidic available for the trip to the JJB Stadium.
The Serbian defender has been suffering from concussion following an accidental clash with Didier Drogba in the defeat at Chelsea last month, but is likely to be back at the heart of United's defence on Sunday.
"I'm hopeful of having Vida," added Sir Alex. "The next two training sessions [Friday and Saturday] are going to be very important for him.
"We'll have had eight days to prepare by the time the game comes round on Sunday which is a bonus," he added.
"The training sessions have been quite light and all the little niggles have cleared up. The mood is very good in the camp."
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