Madrid - Spanish international Sergio Busquets had to be stretchered from the field with a serious looking ankle injury as Barcelona sealed their place in the Copa del Rey 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," said Barca boss Luis Enrique.
"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."
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 and host Manchester City in the second leg of their Champions League last 16 tie in the coming weeks.