Manchester City defender Aymeric Laporte will be out until January or February, says manager Pep Guardiola.
The France centre-back, 25, has had surgery on his right knee after being carried off in the 4-0 win over Brighton on 31 August.
He damaged his cartilage and lateral meniscus in a challenge with Brighton defender Adam Webster.
On Laporte's absence, Guardiola said: "Not long. Five months, six months - next year, January or February."
The defender made 35 league appearances last season, with Bernardo Silva the only City outfield player to play more.
His injury leaves City with just Nicolas Otamendi and John Stones as central defenders, following the departure of Vincent Kompany to become player-manager of Anderlecht in the summer.
Stones could play at Norwich City on Saturday in the 17:30 BST kick-off and Guardiola said the England centre-back "trained good".
Guardiola backs City transfer idea
Meanwhile, Guardiola says his club's proposal for the Premier League to have different deadlines for domestic and international transfers is "a good idea".
Many clubs, including City, were unhappy at the three-week gap between the English transfer window closing and that of the remainder of Europe, believing it offered rival clubs an unfair advantage.
At their meeting in London on Thursday, Premier League bosses discussed whether to revert back to the end of August, rather than closing the window on the Thursday before the start of the season, as has been the case for the past two seasons.
City put forward a compromise solution, with the deadline remaining as it is for transfers within England, but leaving clubs free to sign players from elsewhere in Europe for the remainder of August.
Guardiola said: "It is a good idea.
"I would like to finish the window the day before we start the season. All the managers would want to start with the players we are going to work with. But the other clubs have three weeks. Maybe that is a solution."