Firmino, 27, missed his side's 5-0 thrashing of Huddersfield Town in the Premier League on Friday due to a muscle injury.
Liverpool make the trip to Camp Nou for the first leg of their semi-final against Barca on Wednesday and while Klopp is optimistic over Firmino's availability, the German is not yet certain.
"Bobby trained yesterday [Thursday] completely normally. It was not high intensity, we just had to work on set-pieces a little bit and here and there a couple of things," he told a news conference.
"I didn't see it in training, it happened in the last situation of training and he felt a muscle a little bit.
...aannd breathe, Reds! pic.twitter.com/XvQdoJV2SR— Liverpool FC (@LFC) April 26, 2019
"Now, the official diagnosis is he has a small tear in a small muscle, so apart from the word tear everything else is positive.
"It is Bobby, so he might be ready for Wednesday, but we obviously don't know in the moment. Because it is him, it's rather likely that [he will be] than not, but we will see.
"So, of all the bad news you can get it is pretty much the best, but it's still bad enough that he couldn't play tonight."
Liverpool returned to the top of the Premier League comfortably thanks to braces from Sadio Mane and Mohamed Salah after Naby Keita's first-minute opener.
But they had another injury scare in the second half when star defender Virgil van Dijk appeared to hurt his foot.
However, Klopp dismissed any worries about the centre-back, saying: "No, nothing. I asked him, he said, 'No, no, all good'."