N'Golo Kante was forced off with a hamstring injury in France's World Cup qualifying win over Bulgaria last week and could miss Chelsea's next six games.
The midfield workhorse was replaced just before half time in the 1-0 victory, and early predictions have him out of action for the next two-to-three weeks.
Kante, who won the PFA Player of the Year award last season, will be assessed by Chelsea's medical staff, with the club keen to get their man back to full fitness as quickly as possible.
The French international will definitely miss the Blues' Premier League clash with Crystal Palace on the weekend, but, if Chelsea's worst fears are to be confirmed, he may also be out for their next five following fixtures.
That would see the former Leicester City man miss Roma's visit in the Champions League on October 18, as well as their game against Watford at Stamford Bridge three days later.
Kante would also be out for Everton's visit in the Carabao Cup, their game against Bournemouth at the Vitality Stadium on October 28, and finally, their trip to the Italian capital to face Roma on the last day of the month.
former Blues midfielder Kevin De Bruyne scored the only goal of the game as the home side struggled against Pep Guardiola's swashbuckling Citizens.