Thiago Alcantara faces a race against time to be fit for Monday's Merseyside derby - with Diogo Jota on the brink of a much-anticipated Liverpool comeback.
But the Reds will not take any risks over the fitness of Roberto Firmino, Virgil van Dijk and Arthur Melo after the trio returned to training on the pitch at the AXA Training Centre this week.
Thiago is a major doubt for the Premier League visit of Everton after missing full training on Thursday as he struggles to overcome a hip problem.
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Jota, who hasn't featured since suffering a calf injury in mid-October, made a tentative return to full training last week and has been part of the main group this week.
And Klopp said: "Thiago has some problems. I know the problem but I have to ask if I am allowed to say about it! Hip flexor, stuff like this. So he was not able to train.
"The players are back in training in different stages. Diogo is the closest. He trains now normal already for two days so another three days of training possible for him and then I think he is in contention for the squad I would say, but we have to wait a little bit."
Fimino hasn't featured since before the World Cup in November after picking up a calf complaint, while Van Dijk limped out of the Premier League defeat at Brentford on January 2 with a hamstring injury.
On-loan Arthur Melo, brought in from Juventus on deadline day in the summer, made just a brief substitute appearance before being sidelined with a thigh injury suffered in training.
Firmino and Van Dijk took part in the warm-ups in training on Thursday while Arthur was involved in the full training session.
And of the trio, Klopp added: "Bobby, we have to see how that looks, how he deals with training intensity and stuff like this. Then we make a decision.
"Virgil I don't think is that close already but we will work on that as well. Arthur is probably similar to Bobby I would say."
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