Firmino suffered an abrasion on the cornea of his left eye after being caught by Tottenham defender Jan Vertonghen's flailing arm on Saturday, and it has affected his vision.
Back-up strikers Divock Origi (ankle) and Dominic Solanke (knock) are doubtful and if Firmino does not make it, it means Daniel Sturridge could make his first start in the competition for the club.
"It's good news that it will be close," Klopp said on Firmino. "If the game was today no chance. It's going to be very close, we all saw the picture and we were shocked. It was a painful one. No one wants it or needs it, but he will be fine.
"We only don't know exactly when. The game is what, say 30 hours away or roundabout, so we are not sure how it develops."
Sturridge ready to start for Liverpool
With Solanke and Origi also struggling, Klopp confirmed that Sturridge is ready to start up front for the Reds for their huge opening Champions League night at Anfield.
"He will be ready if Bobby can't play, and Dom and Divock can't, then we are short of options. They got little injuries in the Under-23 game with Swansea. There is no problem with the first line-up.
"We have new injury concerns. We tried to give Divock and Dom a bit of practice. They used it, they scored, but it looks like both of them will not be available for tomorrow.
"It’s not too serious. Div has a little bit of an ankle. He tried this morning and didn’t really work out too well, so he will try again tomorrow morning. With Dom, we have to see. He got a knock and we will see how that develops.
"So not good news in the moment, but we have a lot of players available and when I saw the players yesterday, there were not any other issues."
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