Basel - FC Basel confirmed that Derlis Gonzalez had to go off because he was suffering the effects of a knock on the head during the 1-1 Champions League draw against Porto on Wednesday.
The Paraguayan forward collided with Porto goalkeeper Fabiano when he slid the ball home in the eleventh minute for Basel's goal and was taken off just before the half hour.
"He got quite a knock with the Porto keeper," coach Paulo Sousa told reporters after the after the round of 16 first leg.
"We don't know exactly what happened, it's something we have got to examine. He didn't feel comfortable about continuing the game."