Basel striker Ricky van Wolfswinkel is undergoing treatment for a brain aneurysm that was only discovered after he had scans following a concussion.
The Dutchman, 30, says he is facing “at least six months” out of the game.
The aneurysm is a pre-existing condition and not caused by the severe concussion he sustained near the end of Basel’s Champions League qualifying match against LASK on 7 August.
“I’m very grateful the brain aneurysm got discovered,” he said.
“Normally a brain aneurysm is not discovered in time, only after it has ruptured and caused other damage.”
An aneurysm is a balloon-like bulge in a blood vessel caused by a weakness in the blood vessel wall.
If a brain aneurysm bursts it causes a subarachnoid haemorrhage, which can be fatal or cause extensive brain damage.
Former Norwich striker Van Wolfswinkel was hit in the final minutes of the 2-1 defeat and was taken to hospital after the Basel medical team saw the seriousness of his concussion.
“The doctors made multiple scans and eventually found out that I have a brain aneurysm,” he said.
“The hit I got in the game has absolutely nothing to do with the existing brain aneurysm – this has been there for a long period but I didn’t have any symptoms so we didn’t know it was there.”
He said he was “not able to determine” when he would be back playing following an operation, only that it would not be “for a long time”.
“It’s just clear that it won’t be for at least six months,” he said.
“The returning date will of course depend on the reaction of the brain aneurysm after treatment.
“I want to say thank you to the Basel medical department and the doctors of the university hospital in Basel.
“For now I will focus on my health and recovery to be able to do what I love most as soon as possible and that’s play football.”