Real Madrid's Turkish international Hamit Altintop succesfully underwent surgery to correct a disc problem in his back on Monday in Germany, the Spanish club said.
"Altintop will remain in hospital until Saturday morning," the club said in a statement posted on its website after the operation was "successfully performed" at a Munich hospital.
Real signed the 28-year-old midfielder in May from Bayern Munich on a four-year deal. He struggled for fitness last season at the German side and his appearances were limited.
Altintop is one of three players Jose Mourinho has signed for the new campaign, along with fellow Turkey midfielder Nuri Sahin and Spanish striker Jose Callejon.