Athletic Bilbao are facing a huge sweat ahead of their Europa League crunch with Rangers after Inaki Williams suffered a hamstring strain.
And manager Ernesto Valverde admitted they will have to assess one of their key players ahead of the game.
Athletic got back to winning ways after three goalless draws in a row - including against ten-man Rangers at Ibrox in the first leg - with a comeback 3-1 win over Rayo Vallecano.
But the win was marred by Williams going off in injury time after complaining of a hamstring strain.
And Bilbao boss Valverde is anxious about the fitness of Williams, who has scored 11 goals this season.
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He said: "We'll have to wait and see. It's true that he had a slight discomfort and I didn't want him to continue just in case.
"We had to avoid a dangerous situation, so I decided to tell him to leave the pitch without a substitute to replace him.
"If you're on the pitch, there's always a chance that you make a run and the problem can be bigger."
However, Valverde insisted his team are full of confidence ahead of their visit from Rangers after they ended a goalscoring drought that lasted 334 minutes thanks to a penalty from Oihan Sancet, who later added to the score along with a goal from Nico Williams.
He said: "It was always clear we would get back to scoring goals.
"Sometimes, it just doesn't go your way when you are trying to score goals, but we kept going.
"Leading up to the game against Rangers, what happened against Rayo Vallecano was important to us because a comeback win with some beautifully crafted goals makes people a little happier. "But we won't go into the game with overconfidence."
