Ajax player Abdelhak Nouri received treatment on the field after collapsing during Saturday's friendly against Werder Bremen in Austria, with the Eredivisie club describing the situation as "serious".
In the 72nd minute of the game at Lindenstadion in Hippach, the 20-year-old midfielder lay down on his back inside the Bremen half in clear discomfort.
Ambulances and paramedics then tended to Nouri on the pitch, with a screen drawn around him.
"Emergency services are still [treating] Nouri, players look worried," Ajax tweeted. "It is serious, we [will let you] know immediately if there is more clarity."
A trauma helicopter then landed on the ground to assist the medics treating Nouri and fans were asked to leave the stadium with the match abandoned.