Leroy Sane is facing a lengthy lay-off after suffering anterior cruciate ligament damage, Manchester City have announced.
The German winger, who limped off in the early stages of Sunday's Community Shield win over Liverpool at Wembley on Sunday, is to undergo surgery in the coming week.
The injury comes after a summer of speculation over the 23-year-old's future, with Bayern Munich having been heavily linked with the player.
Sane has been offered a new contract at the Etihad Stadium but has not yet signed. He has two years left on his present deal.
City have not put a timescale on the player's return but Ilkay Gundogan and Benjamin Mendy have both had seasons ruined by similar problems in recent years.
A statement from the club read: "Leroy will have surgery in the coming week.
"Manchester City will provide Leroy with all the support and guidance he needs, and everyone connected with the Club wishes him a quick and full recovery."
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Bayern Munich great Lothar Matthaus is certain Leroy Sane will swap Manchester City for the Bundesliga champions this summer.
Sane is contracted to the domestic treble winners for the next two seasons, but Bayern are eager to lure the 23-year-old back to Germany.
The Bavarian giants are on the lookout for wingers following the departures of Arjen Robben and Franck Ribery, and there have been declarations of interest in Sane from both president Uli Hoeness and chairman Karl-Heinz Rummenigge.
Sane scored 16 goals in 47 appearances in all competitions this season but has struggled to command a regular starting spot in the last few months.
City are thought to be keen to convince Sane - who joined from Schalke for £37million three years ago - to remain in Manchester, but Matthaus believes a return to his homeland is more likely.
"A player who, in my eyes, will enchant the Bayern fans next year is Leroy Sane," Matthaus wrote in his column for Sky Sport.
"I am sure he will move to Munich. If Uli Hoeness publicly reveals that he makes a bid for a player, in the vast majority of cases they arrive at Bayern.
"Guardiola is not really satisfied with him, the player wants to play more regularly and Bayern are looking for at least one wide man after the departure of Robben and Ribery. It would be a win-win transfer for all parties."
As for the transfer fee involved, Matthaus speculated that it could be a record-breaking sum for Bayern.
"Quality always has its price and Sane is more expensive than the previous record transfer of 80million euros for Lucas Hernandez.
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Manchester City's Leroy Sane has been omitted from Germany's World Cup squad.
The 22-year-old was named the PFA young player of the season after a superb campaign in which his contributions to City winning the Premier League title were significant, but it has not been enough for him to travel to Russia.
He was included in manager Joachim Low's initial 27-strong provisional squad but it was unexpectedly announced on Monday morning that he had been cut alongside Bernd Leno and Jonathan Tah of Bayer Leverkusen, and Freiburg's Nils Petersen.
Sane's omission also comes despite 14 goals during the past season and is proving even more of a shock amid the inclusions of Marco Reus, who has long struggled with injuries that meant him missing the past World Cup and Euro 2016, and Leverkusen's Julian Brandt.
He had even played the opening 67 minutes of Saturday's 2-1 friendly defeat by Austria.
Goalkeeper Manuel Neuer, who on Saturday returned from nine months out injured, is therefore among those retained, as are Sane's fellow Premier League representatives Antonio Rudiger, Ilkay Gundogan and Mesut Ozil.
That the 32-year-old Neuer has been included means he is expected to remain as captain, and first-choice goalkeeper, ahead of Barcelona's Marc-Andre ter Stegen.