Phil Foden was forced off at half-time after suffering another ankle problem on a nightmare night for Manchester City.
Pep Guardiola revealed that Foden had complained of an issue with his ankle early on during the 2-1 defeat at RB Leipzig.
The 21-year-old only returned from the same injury last week and City are sweating on the extent of his latest setback ahead of Saturday's Premier League clash with Wolves.
Nathan Ake was also substituted with a back injury, shortly after Kyle Walker had seen red for a petulant kick at Leipzig striker Andre Silva.