Andres Iniesta will be out for around four weeks after suffering a muscle tear in Barcelona's 2-2 draw with AC Milan on Tuesday.
The Spain international pulled up with the problem shortly before half-time and was replaced by Cesc Fabregas.
"Tests have confirmed that the player suffered damage to the femoral biceps of the left leg," the club revealed on their official website.
"The approximate time he will be out of action is four weeks," the statement added.
Iniesta joins team-mates Gerard Pique and new signing Alexis Sanchez on the Barcelona treatment table and will miss games against Osasuna, Valencia and Atletico Madrid amongst others.