Real Sociedad midfielder Luca Sangalli is awaiting further tests in hospital after suffering a mild stroke on Wednesday, the club have told ESPN FC.
Sangalli, 23, had been left out of the Copa del Rey game at Celta Vigo on Thursday because of injury and was taking a university exam in the town of Arrasate when he began to feel unwell.
He called the club doctor and was taken by ambulance to Donostia University Hospital.
"The player is waiting to undergo further tests and is still in the stroke unit," Sociedad said. "He is accompanied by his family at all times.
"He passed all the relevant [preseason] medical tests without any warning signs. The recovery process is indefinite."
Sangalli was promoted to the Sociedad first team in August and has made six league appearances, four of them starts.
The San Sebastian-born player has a degree in mechanical engineering and is studying for a masters in industrial engineering.
Messages of support have poured in, including one from Real Madrid right-back Alvaro Odriozola.
Odriozola, a La Real youth product, posted a photograph on Twitter of him and Sangalli when they were children with the message: "I'm certain you will return stronger than ever because there's no one that can beat you when it comes to fighting. We are all with you, Luki!"