Feyenoord have been informed that forward Romeo Castelen will be sidelined for the first two months of the new season.
The striker picked up an ankle injury in the recent friendly with Middlesbrough and tests have revealed damage to the ligaments.
Doctors have informed the player that he will require a minimum of eight weeks' rest and he will miss games for both club and country, with the Dutch national side set to face Republic of Ireland next week.
Keeper Patrick Lodewijks will miss the start of the Eredivisie season after dislocating his little finger, while Royston Drenthe is a doubt for the game with Groningen after breaking his nose.
Feyenoord have yet to take a decision on whether to offer a contract to Canadian midfielder Jacob Lensky who impressed during a recent trial at De Kuip.