Manchester United boss Louis van Gaal says Robin van Persie could be facing a lengthy period on the sidelines.

The Dutchman limped out of the Liberty Stadium on crutches last week, after suffering an ankle injury in United's defeat by Swansea.

Van Gaal says he's not sure when Van Persie will be able to return.

"I don't think it's very heavy but an ankle problem it takes a long time," said Van Gaal. 

"It's not one week or two weeks, but we have to wait and see."