Manchester City have confirmed Spain midfielder Rodri suffered a knee ligament injury against Arsenal on Sunday.
Rodri was substituted in the 21st minute after he twisted the joint in a collision with Arsenal's Thomas Partey at a corner.
No timescale has yet been put on the player's recovery, but speaking after Tuesday's Carabao Cup win over Watford, Pep Guardiola said he is set for a lengthy spell on the sidelines.
"Still we don't have the definitive [diagnosis] but he will be out for a long time - a while," said the City boss. "But there are some opinions that maybe it will be less than we expected.