Jurgen Klopp admits Fabinho's injury could be a "massive" problem for Liverpool .
The Brazilian midfielder limped off in the first half of the 1-1 draw with Napoli at Anfield.
Fabinho is suspended for the weekend clash with Brighton but is a doubt for next week's Merseyside derby at Anfield.
Georginio Wijnaldum replaced Fabinho against Napoli with James Milner also handed a start in midfield.
Speaking after the clash, the Liverpool boss said: "The biggest things is the Fabinho injury, that's massive.
"It's early and we all hope it's not too serious.
"But it's pretty painful and in an area you don't want to have pain, around the ankle."
Liverpool fell behind to Dries Mertens strike before an equaliser from Dejan Lovren in the second-half.
Virgil van Dijk claimed he was fouled for the Napoli goal with Klopp also shown a yellow card by the referee.
On the clash, he said: "The way Napoli set up, it didn't help that they scored, they could follow their plan all the time, we had to increase pressure all the time. We were not brilliant but we put pressure on them.
"I was not happy with the last 15 minutes of the first half. Second half it was just intense and of course it's not easy, they really defended the goal they had.
"We didn't have the biggest chances, maybe one or two. For tonight it might not be enough but it's still our situation. When we go to Salzburg, if we had done it tonight we would try to win there, so it's still our goal.
Liverpool will qualify for the knockout stages with a draw against Salzburg.
