Last season's top Barclays Premier League goalscorer has been missing since the Champions League win over Shakhtar Donetsk in December that clinched top spot in Group A, sitting out the busy festive period and the three defeats since the turn of the year.
"We’re trying to get Robin back," stated Moyes. "He’s got a thigh strain similar to the one he had at Arsenal [in the second half of the 2007/2008 season].
"He never had an injury all last season. He took a corner against Shakhtar and felt his thigh so it was a freak thing really and not [aggravating] an injury he’d had before.
"It's a different injury. We have to manage it correctly and he’s been to Holland to see a guy he works with there. So we’re doing everything we can to give him the right treatment and get him back as soon as we possibly can. But I don’t want to put a date on his return."
Moyes confirmed on Friday that van Persie would play no part in Saturday's visit of Swansea City, extending the striker's absence to nine consecutive United matches.