Rob Pollard of the club's official website noted the midfielder had to be substituted during Wednesday's Carabao Cup action. Gundogan had only just returned from a devastating knee injury that sidelined him for the bulk of the 2016-17 season, but Wednesday's injury was to the other knee.
While there's no doubting the natural talent Gundogan possesses, his career has been severely hampered by injury issues.
Before moving to City from Borussia Dortmund, he was constantly battling to stay fit, and even when he arrived at the Etihad Stadium, Gundogan was recovering from a dislocated kneecap. After fighting back and returning to fitness, his debut campaign was brought to a premature end when he picked up a knee ligament problem.
Manager Pep Guardiola will be desperate to build a team around the playmaker, as he boasts all the attributes needed to be a big hit in the Premier League.
The 26-year-old has so much quality. In possession he's resourceful with the ball, knowing when to quicken the pace of a game and when to draw some life from it. Gundogan is also penetrative in his play when he does move into the final third.
During his heyday at Dortmund, the German was also a determined worker off the ball. While injuries have robbed him of some of that intensity, he still has the energy to get about the pitch.
It's unclear exactly how much time Gundogan will miss, but according to Pollard, he only suffered minor damage, and he shouldn't be out for long.