Mohamed Salah trained with the Liverpool squad on Monday ahead of the side's Champions League quarterfinal second leg with Manchester City.
Salah was not risked in the weekend's Merseyside derby because of the groin issue he picked up during the first-leg victory over City last week.
The Egyptian spent Sunday at Melwood training with athletic staff and was then present at a session on Monday evening during the 15-minute period the media are allowed to observe.
Speaking about the fitness of his forward at a news conference earlier on Monday, Klopp said: "Not sure, 100 percent.
"Yesterday he was with the athletic coach in training. A 5 o'clock we train at Melwood and then we will see if he can be part of training.
"I would say rather yes than no, but we have to see and then wait for the reaction till tomorrow. Then we will make a decision. That's it."
Andrew Robertson and Alberto Moreno, who were both absent from Saturday's goalless draw at Everton, also took part in Monday's session.
"With Mo, Robbo and Alberto, we have to wait a little bit but of course [we have] big hope they will be back," Klopp had told Liverpool's official website. ""Ben Woodburn is back after a long period and trained yesterday completely normal, which is really good for us."
Meanwhile, there has been no timescale set for Emre Can's return from a back injury that has forced him out of Liverpool's last two games, according to Klopp.
"That is not in the best place," Klopp said about the midfielder's condition.
"[He is receiving] treatment and we're still hoping it will be a little bit quicker than maybe we thought in the first moment. But we cannot say anything else."