Sir Alex Ferguson has described Wayne Rooney's thigh injury as "a blessing" and expects the striker to return fitter.
The England international sustained a gash in his right leg in added time of last Saturday's 3-2 win over Fulham.
Rooney was a replacement after being dropped following a poor opening performance at Everton when Ferguson has accepted he was not fully fit.
But Ferguson, who said he expects the 26-year-old to be out for four weeks, hopes the time out of the team will benefit Rooney.
"The fact it's a gash and not a ligament, muscle or joint injury means he can do a lot of work in the gymnasium," the Manchester United manager explained. "[The injury] is maybe a blessing because he can concentrate on his fitness now."
Ferguson explained his decision to start with Robin van Persie, who scored his first United goal, instead of Rooney against Fulham.
"Rooney wasn't fit," he added. "He said himself that he needed a few games and I wanted to play Robin van Persie from the start at Old Trafford.
"I knew he [Van Persie] wasn't fit either. In fact, it was only because we lost the second goal that I was forced to keep Van Persie on. I couldn't really start the two of them and I wanted to start with Van Persie.
"Wayne is not as advanced fitness-wise as Shinji Kagawa or the other midfield players. It wasn't an easy choice because you are leaving out a player who can get you goals."