Kevin De Bruyne will miss next weekend's Manchester Derby and will be in a race against time to face Chelsea at the start of December after being ruled out for between five and six weeks with a knee injury.
Manchester City have confirmed the news after De Bruyne was substituted during the club's Carabao Cup victory over Fulham, when Cottagers defender Timothy Fosu-Mensah fell backwards onto the Belgian, who was sat on the pitch with his legs stretched out in front of him.
The midfielder will travel to Barcelona for treatment at Dr Ramon Cugat's specialist clinic.
He has already missed 10 games of City's season so far with a ligament injury in his right knee, and although this latest set-back concerns his left knee he is still set to miss another chunk of the campaign.
Speaking after the Fulham match Pep Guardiola said the 27-year-old was just getting back to his best form, having missed most of City's campaign so far.
"He made a huge effort in Donetsk [Kharkiv] against Shakhtar," the Catalan said. "He played a few minutes in a difficult situation against Spurs.
"It was a difficult situation because of the pitch and the conditions and tough physicality but today again he was involved in the offensive and defensive side, in the pace, in the set pieces, the passes and assists.
"Hopefully what happened in the last minutes is not serious."
What games will De Bruyne miss?
The Premier League champions host Manchester United next Sunday, and it remains to be seen whether De Bruyne will be fit enough for the trip to Chelsea on December 8.
He will definitely be out of City's next two games, against Southampton on Sunday and Shakhtar Donetsk on Wednesday, though he will be helped by the November international break following the derby.
City will be back in action at West Ham on November 24 and then travel to Lyon three days later before in December they face Bournemouth and Watford ahead of the game against Maurizio Sarri's men at Stamford Bridge.
If he does miss that clash he could return for the home games against Hoffenheim or Everton in mid-December.