Vincent Kompany has been plagued by injury in recent years and lasted just 35 minutes on his latest return at the weekend before being forced off with blurred vision following a collision with goalkeeper Claudio Bravo.
However, Guardiola has confirmed that the Belgian also picked up a fresh injury problem and now faces another spell on the sidelines.
“He has a problem with his knee. He could be out for weeks,” the Spaniard told reporters.
“We have to try to help him week after week to see if he can play more often. Deciding now is not the right thing.
“He is sad but he is in the best hands. He is travelling to a hospital in Spain so he can recover as soon as possible.”
Kompany has not managed to complete a full 90 minutes in the Premier League since March.