The midfielder pulled up and appeared to have strained his hamstring at the Nou Camp - an injury later confirmed by the club.
Barca coach Ernesto Valverde said: "Iniesta is a unique player, a little like Messi, so it's difficult to find a player who can replace him.
"He is unique in the world in terms of the characteristics he has. We will have to see the extent of the injury. He carried on playing at first so we thought it wasn't too bad, but we're not sure. He was playing incredibly."