The FC Basle striker took a heavy blow to the head late in the first leg of his side's 5-2 aggregate Champions League qualifying defeat to LASK.
Van Wolfswinkel was diagnosed with a concussion but sent to hospital for further testing.
Doctors uncovered an aneurysm that otherwise would have gone undetected and the forward will now take time out from football to have treatment.
"Because of the brain aneurysm, I will need treatment. Having treatment will mean that I won't be able to play football for a long time," Van Wolfswinkel explained on Twitter.
"At this moment, we are not able to determine a date of returning. It's just clear that it won't be for at least another six months.
"The return date will of course depend on the results and the reaction of the brain aneurysm after the operation. The months after will decide when I could be back."