Liverpool are anxiously awaiting a prognosis on Daniel Sturridge after the striker sprained an ankle in training.
The England international has had scans on the problem after limping out of training on Friday.
However, Press Association Sport understands bruising around the affected area means it has been difficult for the Reds' medical team to accurately assess just what the damage is.
Sturridge is out of Sunday's trip to Hull but it may not be until early next week before the true extent of the injury is revealed.
"Liverpool Football Club can confirm Daniel Sturridge will be assessed by the club's medical staff today after the striker rolled his ankle in training," said a club statement.
"Sturridge returned to training at Melwood this week; however, he sustained an ankle sprain which will require further assessment."
The absence of the 24-year-old, who has scored nine league goals this season, means Luis Suarez, also with nine this campaign in just seven league matches, will lead the line on his own at the KC Stadium.
But it is the other end of the pitch where manager Brendan Rodgers has had the most work to do, although he is confident recent defensive lapses were a one-off and not an indicator of a deeper malaise.
The Reds conceded three for the first time since March in a thrillingly open 3-3 Merseyside derby draw at Goodison Park last weekend.
Two of the three goals they let in came directly from set-pieces - a frailty from which they suffered earlier in the campaign - with the third coming in the aftermath of a free-kick.
Liverpool's defensive record is generally good as - even taking into account the three scored by the Toffees - they have let in 13 in 12 matches.
And Rodgers believes last week was an isolated case with mitigating factors which he does not expect to be repeated at Hull on Sunday.
"During the two-week international lay-off, when a lot of the players are away, you're literally only getting your squad back on the Friday and then you're going straight into a big game like the derby," he said.
"That's maybe one of the reasons why it was so open, because of the lack of time both coaches had to work with the players.
"It was a really attacking game that, from a coaching perspective, was probably way too open.
"There were lots of mistakes defensively in the game. There's obviously moments where we probably lost our concentration.
"The game against Everton was unique because at the end of the match it was like a basketball game - there was no organisation.
"But we showed yet again our incredible character that's within the team.
"We're a very hard team to beat and that's very important as any manager will tell you.
"If you can't win a game, then you have to fight not to lose it and that was something that we did against Everton.
"We've worked hard this week on many aspects of our game. You move on and we go into the game on Sunday prepared for a hard game."
Rodgers believes it is better to go out looking to be positive and win games than trying to just be difficult to beat, although he accepts that requires a different mindset from the players.
"When I came in here, the big challenge was to score goals. I think everyone recognised that was an issue within the team.
"This year we are one of the highest goalscorers in the league and that's what wins you football matches.
"At times we are going to have to take a risk - that may result in you conceding another goal but I will always be offensive and creative in the approach.
"The defensive side has been quite solid but we can always be better."
Hull will obviously try to exploit any perceived weakness in Liverpool's defence and as the best performing of the three promoted sides Rodgers will not take them lightly.
"We know it's going to be a very difficult game," added the Reds boss.
"Of the teams who have been promoted, they've done really well and they look to be heading on course to be a team in the middle of the table, so that tells you that it's going to be a very difficult game for us.
"But our confidence is high and out spirit is very strong at the moment."