Schalke's Klaas-Jan Huntelaar has been ruled out of action due to an eye problem, with the German club unsure as to when the striker will return.
Huntelaar, 29, is currently being treated by an eye specialist after rupturing a blood vessel in his left eye, forcing him to miss out on Netherlands' 1-1 friendly draw with Italy on Wednesday.
The former Real Madrid man will not be able to return to training with the Royal Blues until he has been given the all-clear, and no time limit has yet been placed on his return.
Netherlands manager Louis van Gaal said earlier in the week that the problem was "nothing really serious". However, Schalke's general manager Horst Heldt does not agree.
"Something like this can be good in two days, but it can also take considerably longer," he said.
The striker has been struggling for form lately, not having scored for his club since the end of November.