Manchester City's Nico O'Reilly suffered an injury in the warm-up ahead of Manchester City's match at home to Coventry City.
Despite enjoying the majority of his success at left-back last season, O'Reilly has started the new Premier League campaign in a centre-midfield role.
The 21-year-old has flourished alongside Elliot Anderson at the start of Enzo Maresca's reign at the Etihad Stadium.
O'Reilly has played a key role in back-to-back wins as Maresca begins the unenviable task of following legendary former manager Pep Guardiola.
The England international was set to start against Coventry but he looked uncomfortable as he left the pitch holding his back following the pre-match preparations.
O'Reilly was replaced in the starting line-up by deadline day signing Enzo Fernandez, but City supporters will be hoping that one of their key players is not absent for long.
When is Nico O'Reilly expected to return from injury?
Maresca will be hoping that O'Reilly has not pulled a muscle in his back, which could rule him out for up to four weeks.
However, a mild strain is likely to result in O'Reilly missing up to two weeks.
The injury could see O'Reilly miss City's opening UEFA Champions League fixture against Porto on Tuesday, as well as the Manchester derby at Old Trafford on Sunday.
An EFL Cup tie at home to Norwich City a week on Thursday is likely to give Maresca an opportunity to rest players, which could mean that the home game with Sunderland on 20th September could be targeted for O'Reilly's return.
A more severe muscle injury could result in O'Reilly being absent until after the international break, which would also include England's four-game itinerary.
The first game for the Cityzens after the international break sees them travel to Liverpool on 11th October.
