Wayne Rooney could return in time for the start of Manchester United's Premier League campaign on 17 August after recovering from a virus.
The 22-year-old contracted the mystery illness on United's tour of Nigeria and returned to training on Friday.
"We've got a big job to do to get Rooney ready," said Sir Alex Ferguson.
"With seven or eight days training we might make it. He is doing much better, the medical reports are good and we feel that he's clear of the virus."
The England international will miss Sunday's Community Shield match against Portsmouth.
Midfielder Michael Carrick, who was suffering from the same unnamed illness, is set to feature in the Wembley fixture.
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He also added that the squad had all taken malaria tablets ahead of the trip to Africa, while the club confirmed that the touring party have all had the required yellow fever vaccinations within the past 10 years.
Rooney's potential absence leaves Ferguson facing a selection dilemma ahead of the opening match of the season at home to Newcastle.
Cristiano Ronaldo will miss the first two months of the season following ankle surgery, winger Nani is suspended while midfielder Anderson is on Olympic duty with Brazil.
Rooney's problems could also reignite Ferguson's interest in signing Tottenham forward Dimitar Berbatov.
As it stands, Ferguson has only Carlos Tevez, untested youngster Fraizer Campbell and Louis Saha to choose from up front.
"I don't know whether we will have a team ready," said Ferguson. "Nani is suspended, Anderson is in the Olympic Games.
"(Michael) Carrick's come in this morning and he may play a part of the game on Sunday."
Rooney had sat on the sidelines when Manchester United played FA Cup winners Portsmouth in a friendly in Abuja on 27 July.
He then missed his club's two subsequent pre-season fixtures against Espanyol and Peterborough.
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