The 40-year-old had missed a press conference earlier in the week after catching what he called a nasty virus.
Vincent Kompany was rushed to hospital by an emergency medical team on Friday after collapsing during a training session, Bayern Munich confirmed. The club said the former Manchester City defender had been watching a session involving the reserve team at Bayern's Sabener Strasse headquarters when he collapsed.
Bayern said Kompany is undergoing thorough examinations at the hospital and will remain under medical care. The club has not yet offered further update on his condition.
The 40-year-old had already missed training and a press conference on Tuesday ahead of Bayern's Champions League draw against Arsenal at the Allianz Arena. Speaking after that match, Kompany explained his absence, saying he had caught a nasty virus the previous week and had ignored the warning signs. "I caught a pretty nasty virus last week, and of course I didn't listen to my body -- and then at some point my body just said, 'enough is enough!'" he said.
No timeline has been given for his return to the touchline, and Bayern have not commented on how his hospitalization might affect the team's preparations.