Van Persie has been working his way back to full fitness after spraining his knee during Manchester United's Champions round-of-16 tie against Olympiakos in March.
The 30-year-old was ruled out for six weeks and returned to Holland to undergo rehabilitation, though he came back for the final three Premier League games of the season, scoring against Hull City.
Van Persie has played no more than 80 minutes in each of the Netherland's past two international friendlies against Ecuador and Ghana but he has scored in both games and Van Gaal is confident his star man will be fully fit for the World Cup finals.
"He is not 100 per cent, but we have two weeks to go. I think he will be 100 per cent," the Oranje boss said ahead of Wednesday's clash with Wales.
"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.
"Then he played two matches of 20 or 30 minutes and the last match 70 minutes.
"We did not expect that as the injury was bad."
Netherlands will come up against defending champions Spain, Chile and Australia in Group B at the showpiece event, which kicks off on June 12.