Barcelona's French international Eric Abidal was scheduled to undergo a liver transplant Tuesday, a club spokesman said without confirming whether the operation had begun.
"I confirm that the operation was scheduled for today but I don't know whether it has started," the Barcelona spokesman told AFP.
"We have not received any information to the contrary. We are in the hands of the doctors, waiting to see what they will say."
Barcelona announced March 15 that the 32-year-old defender would have a liver transplant "in the coming weeks", nearly a year after the player had a tumor removed from the same organ.
The club did not give any indication of how long he would be out of action but the operation puts him in doubt for the French team in the June 8-July 1 Euro 2012 finals in Poland and Ukraine.
Organ transplant specialist Rafael Matesanz had earlier told the Marca newspaper that it would be "very difficult" for Abidal to play again.