Alisson Becker has sustained a hamstring injury and is not expected to return until after the next international break in November.
This means Liverpool will be without their No 1 goalkeeper until November.
He is expected to miss matches against Chelsea, Arsenal, Brighton, and Aston Villa in the Premier League, as well as two Champions League fixtures against RB Leipzig and Bayer Leverkusen.
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Liverpool also face Brighton in the Carabao Cup, but Caoimhin Kelleher featured in the last round.
He was substituted in the second half of Liverpool's 1-0 win over Crystal Palace at Selhurst Park on Saturday. With regular No 2 Kelleher unavailable through illness, 23-year-old Vítezslav Jaros made his Premier League debut, keeping a clean sheet.
Kelleher did, however, recover in time to join up with the Republic of Ireland squad for the October international break.
Analysis: Alisson a big Liverpool miss as the Premier League's best GK
Sky Sports' Sam Blitz:
"Liverpool face a crucial run of games coming up - with back-to-back league games against Chelsea and Arsenal straight after the October international break. Arne Slot's side will face some of the most in-form attackers in Bukayo Saka and Cole Palmer in those games, so missing Alisson for the next month is a major loss.
"The Brazilian has produced big saves in big moments for Liverpool down the years but Alisson's biggest quality has been his consistency.
"Even with this season in its infancy, Alisson stands out as statistically the best goalkeeper in the division. Liverpool's solid defensive block under Slot means he hasn't faced much in terms of high-quality shots, but when he is needed, he is extremely reliable.
"It is why Alisson has only conceded two Premier League goals this season. The next best record is Arsenal's David Raya and Nottingham Forest's Mats Selz with six.
"Caoimhin Kelleher has stepped up plenty of times for Liverpool in recent years and made seven saves to keep a clean sheet when Alisson was absent against Bournemouth earlier this season.
"But with Liverpool also facing Brighton twice, Bayer Leverkusen, Aston Villa and Real Madrid before the end of December, this is a big spell in the season that the Irish goalkeeper will have to oversee."
Liverpool's fixtures until end of November
- October 20: Chelsea (h) - Premier League, live on Sky Sports
- October 23: RB Leipzig (a) - Champions League
- October 27: Arsenal (a) - Premier League, live on Sky Sports
- October 30: Brighton (a) - Carabao Cup, live on Sky Sports
- November 2: Brighton (h) - Premier League
- November 5: Bayer Leverkusen (h) - Champions League
- November 9: Aston Villa (h) - Premier League
- November 24: Southampton (a) - Premier League, live on Sky Sports
- November 27: Real Madrid (h) - Champions League
(c) Sky Sports 2024: Liverpool goalkeeper Alisson Becker's injury set to rule him out until after November internationals
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