The Brazilian was forced off in the first-half at Old Trafford on Sunday, having first attempted to carry on through the pain.
“[It] looks good. We were obviously lucky, it’s not as serious as we thought in the first moment; if Bobby leaves the pitch it’s a bad sign.
“Because we play tomorrow [againt Watford] it will be very close, but there’s a very big chance for the derby [on Sunday].
“Because its Bobby I would say yes [there’s a chance] but I don’t know if I’d use that chance.
“Writing Bobby off is a big mistake, he recovers pretty quick.”
Firmino was seen leaving the ground aided by the help of crutches, with manager Jurgen Klopp later saying he thought the injury was a “catastrophe for us”.
The 27-year-old had a scan to determine the extent of the injury at Spire Hospital in Liverpool on Monday, and is likely to miss Wednesday night’s fixture with Watford.
According to Dominic King of the Mail, Firmino is also a doubt for Liverpool’s visit of Goodison Park to face Everton on Sunday.
Firmino’s absence would a huge blow for Klopp, who will be hoping the Reds can kick on in the title race after regaining a one point lead over Manchester City after their draw at Old Trafford.
It will be intriguing to see the boss shapes his side without Firmino, with Mohamed Salah a possible contender to lead the line again, moving from his right-wing role.
Salah has an exceptional record against Wednesday’s opponents and his redeployment would allow Xherdan Shaqiri to come back in to the side from the right.