Liverpool manager Jurgen Klopp faces an anxious wait to see if Virgil van Dijk will be fit for Saturday's top of the table Premier League clash at Chelsea on Saturday.
The world's most expensive defender has been the foundation around which Klopp's men have greatly improved their defensive record since the giant Dutchman joined from Southampton in January for £75 million ($98 million).
However, Van Dijk is still feeling the after-effects of a rib injury that forced him off in a 3-0 win over his former club last weekend.
"With Virgil we have to wait. He hasn't trained so far with the team but I can't say any more about that," said Klopp on Friday.
"Virgil is a world-class player, there is no doubt about that, and if you miss a world-class player it is not cool."
Liverpool are looking to stretch their perfect Premier League start to seven games and get revenge on Chelsea for a 2-1 League Cup defeat to Maurizio Sarri's men on Wednesday.
However, Klopp may be reluctant to risk Van Dijk with a Champions League trip to Napoli to come on Wednesday and the visit of Premier League champions Manchester City next weekend.
"Before we started it was clear that a game against Chelsea at Chelsea will not be a children's birthday or whatever, that's pretty intense," added Klopp on the demands of three huge games in eight days.
"Then we go to Naples which is a tough place to go and then Man City coming.
"It's an interesting month, to be honest. But so far, so good and the boys are fully in it and ready to go."
Both sides made eight changes for the first of two clashes in four days in midweek, but Eden Hazard came off the bench to decide the tie with a moment of individual brilliance to score the winner.
The Belgian has already scored six goals this season and will be the key player if Chelsea are to mount an unexpected title challenge to Liverpool and City.
"I know exactly how good he is," said Klopp.
"Eden Hazard is a special player, obviously, and he enjoys these one-on-one situations or one versus two or three situations, he enjoys it.
"I didn't need that game to know about Eden, it was already clear before."