Kevin De Bruyne could be sidelined for up to a month, according to reports.
More will be known on Monday but initial concerns are that the Belgian may be missing until at least mid-October and perhaps even until the end of next month.
Regardless of how long De Bruyne is out, Pep Guardiola expects his squad to cover any length of absence.
"From the way he reacted, I think it's a muscular injury but I am not a doctor," Guardiola said after the match.
"It's a pity as Kevin is an important player for us. That's why we have to have a big squad as everyone will help us."
If the 25-year-old is out of action for as long as expected, he will miss Wednesday's Champions League trip to Celtic, next weekend's key Premier League clash with second-placed Tottenham Hotspur, plus other league meetings against Everton and Southampton, the October 19 meeting with Barcelona at Camp Nou and Belgium's World Cup qualifiers against Bosnia-Herzegovina and Gibraltar.
There is a slight chance he may also be in doubt for the EFL Cup derby with Manchester United at Old Trafford on October 26.