"It was a really serious injury in the calf and it's now much better. That's good for us and good for him but we don't know exactly.

"The target was always after the next international break he could be ready but we don't know. Hopefully everything will be fine for the rest of the season, that's the plan."

Adrian has filled in between the sticks in Alisson's absence and, although he has only conceded three goals in four league games, he has looked decidedly shaky at times.

Klopp is, though, hopeful midfielder Naby Keita will soon be available. He has not played since the Community Shield because of a hip/groin injury.

"Naby is close," said Klopp. "He could be in training when we come back from Napoli next week."

Liverpool will aim to continue their flawless start to the Premier League season when they face Newcastle at Anfield on Saturday. Victory would make it 14 league victories in a row across two seasons.

Klopp's side are the only team yet to drop a point, and Newcastle can expect to face an energised duo in Mohamed Salah and Sadio Mane after both were without games during the international break.

"It was perfect for the boys who didn't have to go," said Klopp. "They are refreshed and hopefully we can use that."

Newcastle picked up four points from their first four games after a tumultuous summer following the departure of Rafael Benitez as manager and appointment of Steve Bruce.

A 1-0 victory over Tottenham was a major boost for Bruce, and Klopp has been impressed by the Magpies' start.

"Off season it was really difficult with Rafa leaving," said the German. "For Steve for sure a difficult job. He did fantastic so far – close games and good results as well.

"(They're) very difficult to play. They kept pretty much the same style as last year. I think 24/25 per cent possession at Tottenham but always really good, scored a wonderful goal, defended with a big heart and good organisation. That's what we had to prepare for and that's what we did. It will not be easy."

On Monday, Liverpool will head to Naples for their first Champions League game of the season amid concern over the state of the Italian club's dressing rooms.

Napoli played their first two games of the season away from home to allow renovation work to be completed and boss Carlo Ancelotti said he was shocked by their condition on returning to the stadium.

Klopp said: "I trust UEFA enough to think that they will sort something and we will have a shower and a space where we can change. I hope it will be organised like this but I don't know.

"I don't want to make it bigger than it is. If it would look like it looked on a few pictures we saw, that would be not too cool, but, as long as the pitch is still there and all the rest as well then we could play.

"We cannot change it so we only go there and accept the circumstances and go out and play football."