Firmino had a resigned look as he made his way off the field and the manager offered an update on his fitness ahead of Liverpool’s trip to West Ham.
“Bobby is not good news with a serious hamstring injury, really unfortunate,” Klopp told the club’s official website.
“We don’t know exactly how long he will be out but it will be not now after the international break directly. We have to work on that.”
When Liverpool return from the break they have 12 games remaining in the calendar year and even a minor injury could see a player miss three matches and the hope be that Firmino can have a swift and trouble-free recovery.
“Losing Bobby Firmino is a blow. It’s weeks, more than four and that’s what I would consider a serious injury.”
The midfield department will remain without Curtis Jones after a freak training ground incident that led to a finger in the 20-year-old’s eye, but the return of Fabinho and Thiago eases what had been a growing injury list.
“Curtis is a completely different story [to Firmino], he was very unlucky in training – he got a finger that scratched the eye,” Klopp added.
“I had a lot of injuries to players in my career, that was not involved. He is on the way back but we have to see how long exactly.
“He will be back after the international break, for sure, but in the international break we have to see when he can start doing proper stuff again.
“And Joey [Gomez], hopefully after the international break as well.
“Fab was clear – he was not that long out – that he can maybe go, how we decided then 60 minutes.
“And swapping that with Thiago was probably exactly the right thing to do, now they should be both a big step ahead, so all good.”