The Brazil international was replaced by Vitezslav Jaros on 79 minutes after he could no longer continue the game as the visitors managed a 1-0 victory against the Eagles. The club do not expect the goalkeeper to be back before the next international break which is in the middle of November.
This is a huge blow for the league leaders who have a number of tough games coming up, including ties against Arsenal, Real Madrid, Chelsea, RB Leipzig and Bayer Leverkusen which all occur before Alisson is set to be fit again.
Reds boss Arne Slot spoke on the injury blow and how his replacement is already set in stone, ready to play despite not coming on against Palace.
"It is quite clear then that he (Caoimhin Kelleher) is the number two," said Slot following the game at Selhurst Park.
"Otherwise, the last time Alisson was injured I would have played Vit, but I played Caoimhin. So Caoimhin is the number two and did really well."