"We all saw the picture and we were massively worried. But all these worries are away so he will be fine. (But) if he will be fine for tomorrow, I don't know in the moment," Klopp said on Monday.
"We are obviously in close contact with him and it improved already – but in this moment I can't say if he will be available for (Tuesday)," he added.
Should Firmino be unable to take his place at centre forward, then Daniel Sturridge is the most likely to take his spot.
Klopp said that forwards Dominic Solanke and Divock Origi were both ruled out for the visit of PSG due to injuries picked up on Sunday playing for the club's Under-23 team.
Another decision Klopp will have to make is whether to recall Jordan Henderson to central midfield or stick with Naby Keita and Georgino Wijnaldum, who featured in Saturday's win at Tottenham.
Henderson, who skippered Liverpool last season on their run to the Champions League final, where they lost to Real Madrid, has been given a restricted start to the campaign after returning late to pre-season after the World Cup.
The England international said he had no problem with the selection choices made by Klopp.
"I came back later than everybody else so I can't expect to come straight back in," he told a news conference.
"The lads have worked so hard in pre-season. I can see the benefits already. The rhythm they have - they're at a very, very high level. They're winning games.
"It's normal for me that I'm not playing, I can accept it. Just means I have to keep working hard and take my chance when it comes," he added.
Liverpool have won all five of their Premier League games so far and Henderson said he needed a break after a marathon campaign last season.
"I totally respect the players around us - how well they're playing - and the manager. He's always right. I've tried to use this period to refresh my body and mind because last season was long."
(Reporting by Simon Evans, Editing by Christian Radnedge)
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