AZ Alkmaar are fearful that defender Barry Opdam will be sidelined for some time with a knee problem.
The stopper limped off 30 minutes into AZ's weekend draw with Heracles Almelo and it is feared he has suffered serious ligament damage.
"I am afraid he will be out for many weeks," AZ coach Louis van Gaal said after the game. "It looks like a serious injury."
Opdam is set to undergo a series of tests this week, but the club fear he has sustained ligament damage to his knee.
The news will come as a blow to AZ who are still fighting for honours both domestically and in Europe, as Opdam had only recently returned from a hamstring injury.