City meet Shakhtar Donetsk in the Champions League tomorrow night.
Gabriel said, "I'm not happy because Sergio is injured, I don't like it when my friends are injured, but I'm ready to play, I show that every time in the training session.
“It's not easy [to be on the bench], I want to play but I want to improve my football, that's why sometimes I'm not happy.
“When I decide to come to City I know it's going to be hard because we have Sergio, who is the top scorer of the club. I think I have a chance to play with Pep, with top players here, at a big club."