Wayne Rooney is doubtful for Manchester United's Premier League game against Sunderland on Saturday but Dutch striker Robin van Persie could return, interim manager Ryan Giggs said on Friday.
Rooney is one of several players who have picked up a bug this week.
"Wayne has also got a tight groin so obviously with the bug you have to be careful because his immune system is down," Giggs told reporters.
"Wayne, being Wayne, wants to play, so we'll monitor it over the next 24 hours."
There was better news of Van Persie, whose hamstring injury has kept him out for more than a month since scoring a hat-trick in the Champions League victory over Olympiakos.
"Robin's back in training and has looked really good this week," Giggs said. "Whether it's too early tomorrow we'll have to see."
The 40-year-old Giggs, who has played nearly 1,000 times for his only professional club, declined to say whether he would pick himself in a rare example of a player-manager appearing in the Premier League.
Giggs has not played since April 1 against Bayern Munich.
United won his only match in charge, 4-0 against relegation-threatened Norwich City last weekend.
With the club widely reported to be in final negotiations with Netherlands manager Louis van Gaal, Giggs's future is in doubt.
"Nothing's changed," he said. "It's until the end of the season and we'll chat when that's over. My main concentration is on the remaining three games.
"I have a lot to think about and whether to continue playing."
He admitted that off-field tasks were taking up much of his time in the busy end-of-season period.
"The only peace and quiet you get is when you're on the training pitch," he said.
"As soon as you come back into the office you've got meetings and calls. For example this week has been planning pre-season, which has been testing, as we have to wait and see about the Europa League and permutations with that.
"It's an important time for young players, extending contracts, loan players coming back and players that need their future sorting out."
United are due to tour the United States at the end of July, which could clash with Europa League qualifying.