Aymeric Laporte is set to be out for three or four weeks with a hamstring strain, meaning he will miss the Champions League last-16 second leg against Real Madrid.
French defender Laporte had to be replaced by Fernandinho 33 minutes into Wednesday's contest at the Santiago Bernabeu after appearing to suffer the injury in a collision with Karim Benzema.
City went on to win the match 2-1 and give themselves a significant advantage ahead of the second leg in Manchester on March 17, but Laporte is unlikely to be available for that clash.
Speaking at a news conference on Friday ahead of Sunday's EFL Cup final against Aston Villa, Guardiola said: "It's a hamstring injury.
"Normally it is three weeks or a month [out of action]. We try to avoid it, but it has happened. It happens sometimes."Published 28 Feb 2020, 19:14 IST