Barcelona eased through their Copa del Rey semi-final but suffered an injury to star midfielder Sergio Busquets.
The Spanish international had to be stretchered from the field with a serious looking ankle injury as Barcelona sealed their place in the final with a 3-1 win over Villarreal on Wednesday.
"Busquets has a high ankle sprain in his right ankle," Barcelona said in a statement.
"He will undergo more tests on Thursday to discover the exact extent of the injury."
The 26-year-old had his ankle stood on by Villarreal midfielder Tomas Pina in the build-up to the hosts equaliser on the night scored by former Barca man Jonathan dos Santos.
"It is the bad news of the night without a shadow of a doubt," Barca boss Luis Enrique added. "I can't give a diagnosis before the doctors look at him. We know he will be out for a while, how long the doctors will decide."
Neymar scored an early opener before Dos Santos sent the sides in level at the break.
Pina was then shown a straight red card 20 minutes into the second half for another heavy challenge on Neymar.
Luis Suarez made it 2-1 before Neymar rounded off the scoring to seal a 6-2 aggregate victory.
However, the loss of Busquets could prove an expensive price to pay for a place in the final for the Catalans as they face Real Madrid in a crucial La Liga clash before hosting Manchester City in the second leg of their Champions League last 16 tie.