Netherlands coach Van Gaal was appointed as Moyes' successor in May after a dismal campaign that saw United finish seventh in the Premier League.
Van Persie struggled with injuries throughout last season but was given permission by Moyes to train in Holland prior to his sacking.
And Van Gaal feels the striker will be 100 per cent fit for their World Cup opener against Spain on June 13 partly due to his work in the Netherlands prior to the World Cup.
"He is not 100 per cent, but we have two weeks to go. I think he'll be 100 per cent," TheManchester Evening News quotes him as saying.
"He is coming out of injury but we built him already up in our federation, our medical department.
"It was under the permission of David Moyes. So we could control him, he has worked very hard."
Van Persie has scored in both of the Netherlands's pre-FIFA World Cup friendlies against Ecuador and Ghana.
