Madrid - Spanish international Sergio Busquets had to be stretchered from the pitch during Barcelona's Copa del Rey semi-final, second leg match against Villarreal on Wednesday with a serious looking ankle injury.
"Busquets has a high ankle sprain in his right ankle," Barcelona said in a statement.
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"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.
Neymar had opened the scoring and given Barcelona a 4-1 lead on aggregate after just three minutes from Lionel Messi's cross.
Pina was then shown a straight red card 20 minutes into the second-half for another heavy challenge on Neymar.
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 and host Manchester City in the second leg of their Champions League last 16 tie in the coming weeks.