Two stadium stewards were left injured after being attacked by fans ahead of the Round of 16 Europa League game between Athletic Bilbao and Marseille, the Spanish daily newspaper El Correo reported.
One of the stewards was stabbed in the neck, while the other suffered a knife wound in the arm during the violence that erupted inside and around the San Mames Stadium in Bilbao.
According to the attending medics, the injuries were life-threatening.
A video of the clashes shows the visiting fans fighting with the stadium security and throwing flares towards the Bilbao supporters.
Three Marseille supporters were arrested.
Thursday’s incident comes less than a month after a police officer died of a heart attack in Bilbao on February 22 during fan violence involving Spartak Moscow.
Five policemen and four Russian fans were also injured that incident.