The 24-year-old England striker could miss the final two games of his title-chasing club's domestic season with a groin problem.
Rooney had scored a career-best 34 goals for the Red Devils in all competitions this season before being confined to the sidelines by first an ankle injury and now a fresh problem.
However, despite admitting his frustration at being confined to the sidelines, Rooney believes the enforced lay-off could ultimately help him arrive at the World Cup in South Africa fully refreshed.
"I'm pleased to have done well in a World Cup year but it's been a difficult last couple of months injury-wise," he said.
"I'm disappointed to have missed a couple of games over the last few weeks.
"No-one likes watching football if you're a player, it's difficult knowing you can't influence the game. It's frustrating.
"But if there's any consolation I'll probably be fresher for the World Cup, which will be good for me."
Rooney was named Professional Footballers' Association Player of the Year on Sunday evening.
Source: DSG
