Netherlands captain Robin van Persie may miss Wednesday's World Cup semifinal against Argentina, as he is struggling with an upset stomach.
Van Persie, who has looked off the pace during the Oranje's two knockout-stage matches so far, trained away from the main group of players on Tuesday along with defender Daryl Janmaat.
Netherlands vs. Argentina: July 9, 4 ET (ESPN and WatchESPN)
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And Netherlands coach Louis van Gaal confirmed on the eve of the Albiceleste game in Sao Paulo that the striker, who has scored three goals in Brazil, is a serious doubt.
"He has a stomach problem, an intestinal problem. I don't know [if he will play],'' Van Gaal told his prematch news conference. "I will decide [on Wednesday].
"Van Persie is our captain, so he is very important to us. In principle my captain always plays, but he has to be fit.
"In general, I give the players two days to recover, so if you have one day less it's an issue, a problem. But a top athlete can perform, so my players will be in shape.''
There was better news for midfielder Nigel de Jong, who went through his paces along with the rest of the team in training in a bid to regain his place in Van Gaal's starting XI.
De Jong injured his groin early in the second-round victory over Mexico, and there were fears his tournament was over after the Dutch team said he likely would need two to four weeks to recover.
But Van Gaal said: "If his reaction is good and he can play, then the miracle can come true."
There was further good news for the Netherlands coach on Tuesday, as injury doubts Ron Vlaar and Leroy Fer both trained.
Meanwhile, Van Gaal's decision to bring on Tim Krul in the 120th minute of the quarterfinal win against Costa Rica was hailed as a masterstroke.
Krul saved two penalties after replacing Jasper Cillessen, but the Newcastle man will not start the semifinal.
"No. I ruled that out straight away,'' Van Gaal said when asked whether he would play Krul.
"Jasper is doing a wonderful job, it was just that stopping a penalty is something that the others [Krul and third choice Michel Vorm] are better at.''
Although Argentina are yet to hit peak form in Brazil, they are the bookmakers' favourites for the match at the Arena Corinthians.
Van Gaal, though, believes there is nothing between the two sides.
"I don't think there is a favourite,'' he said. "The countries are at the same level. It's a 50-50 match and we have to be a bit lucky too.''
Key to Netherlands' chances of making the final will be how they deal with the threat posed by Lionel Messi, who has finally transferred his domestic form with Barcelona onto the international stage.
"He has been voted the world's best player before, and you don't get that for nothing,'' Van Gaal said. "He has always found it hard to show his form at international level.
"He wants to do it at this tournament, and we want to stop him. That will be a challenge.''