Report: Ron Vlaar is doubtful for Netherlands vs. Argentina semifinal clash

Dutch defender Ron Vlaar missed a light training session on Sunday to rest his aching knees, and now Agence France-Presse is reporting that the Netherlands may be without the center back for Wednesday's World Cup semi-final against Argentina.

Due to Louis van Gaal's flexible use of formations and starting XIs throughout the tournament, there are several options to replace the Aston Villa defender. 

Feyenoord defender Terence Kongolo could start in Vlaar's place, as could Ajax center back Joel Veltman. Another scenario could see the return of Daryl Janmaat to the lineup at right wing-back, with Dirk Kuyt going back to a left wing-back position. This would shift the rest of the left side of the back line toward the center. Perhaps Memphis Depay, who was rumored to be preparing to play a left wing-back role against Costa Rica could fill that position as well.

The options are seemingly limitless, just as van Gaal wants it.