Liverpool midfielder Lucas Leiva will be ruled out for at least five weeks, manager Jurgen Klopp revealed.
The Brazilian missed Wednesday's impressive win against Manchester City after suffering a thigh injury against the Citizens during the Capital One Cup final.
Striker Daniel Sturridge is however fit to face Crystal Palace on Sunday.
"Lucas is really unfortunate," Klopp said.
"It's a little bit more serious, I've never heard about an injury you get like this, from a penalty, but it was only because he was a little bit injured before.
"He didn't feel too much but after the shot it was done. [It's a] quad – I don't know exactly but five or six weeks [out], not too good.
"[Mamadou Sakho] did a little bit today for the first time, but we didn't really do a lot because it was the second day after a game.
"The only session we have is tomorrow and we have to see how he is then, but today was the first day he did a little bit more.
"[And] Daniel Sturridge trained completely normally yesterday."