(Adds quotes, details, changes byline)
By Peter Rutherford
SAO PAULO, July 8 (Reuters) - Netherlands striker Robin van Persie is a doubt for Wednesday's World Cup semi-final against Argentina after coming down with stomach problems, coach Louis van Gaal said.
Van Persie, the Netherlands' joint top scorer with three goals in the tournament, has been training separately from the squad and Van Gaal said he would not be able to make a decision on his fitness until the day of the game.
"He has some stomach problems, some intestinal problems, so it's best not to train him," Van Gaal told reporters at the Corinthians arena on Tuesday.
When asked if the 30-year-old forward would be fit to face the South Americans, Van Gaal replied: "I don't know. Tomorrow I'll have to take all these decisions but I can't do that today.
"We have more than a day to go and Van Persie is a very important player for us."
Van Gaal, who will take over as manager of Van Persie's club Manchester United after the World Cup, said the strapping seen on the striker's leg was nothing unusual.
"Van Persie is our captain so in that capacity alone he is very important," he added. "He only has stomach problems and he has some plasters around his leg, he always does."
The 30-year-old started the tournament with a bang, scoring twice against Spain including a diving header which is a candidate for goal of the tournament.
He also netted against Australia but picked up a second yellow card, ruling him out of the Netherlands' final Group B game against Chile.
Van Persie was substituted late on against Mexico in the last 16 and his replacement, Klaas-Jan Huntelaar, scored the winner from the penalty spot in stoppage time as the Dutch battled back from a goal down.
In the quarter-final against Costa Rica, Van Persie missed a series of chances but scored the Netherlands' first penalty in a shootout victory that sealed their place in the semi-finals.
DE JONG MIRACLE?
Van Gaal is also sweating on the fitness of defender Ron Vlaar, who has started every game at the World Cup. The 29-year-old is reportedly struggling with a knee injury.
"He was also tested today and we'll have to wait and see what the reactions are," said Van Gaal. "I can't say anything about that."
Although midfield hard man Nigel de Jong has returned to training just a week after suffering a serious groin injury against Mexico in the quarter-finals, Van Gaal said it would be a "miracle" if he was fit to face Argentina.
"He tried out today and we'll have to wait and see how it looks tomorrow because if you want to return to the pitch so quickly you'll always have a reaction," he said.
"If these reactions are good, or such that he can play football, then that miracle will have taken place."
The Netherlands are looking to return to the World Cup final after losing to Spain in Johannesburg four years ago.
(Additional reporting by Mike Collett-White,; Editing by Ed Osmond)