This is the view of Reds inspector and ex-midfielder Danny Murphy, who saw Liverpool beat Serbia 2-0.
It was their second defeat in the Champions League and came with Firmino rested from the original XI.
The Brazilian has fought against this term in relation to last season, noting just two in the Premier League so far.
Liverpool is unbeaten in the league and faces Fulham today (12pm) as they look to put pressure on Chelsea and Manchester City.
Firmino is likely to return to the side for the clash against Fulham fighters in Anfield.
And Murphy believes the Belgrade red star loss has shown Jurgen Klopp the value of the front.
"One thing we learned, if we did not already know, is how important Roberto Firmino is to this Liverpool team," Murphy writes in his column for Mail.
"He was resting on the bench and from the moment he came in half, Liverpool was already 2-0 down.
"He's been doing a great job at the club and he's been very impressed.
"Firmino is technically very good, but what is based on being at the top of his game is of course right because his production is enormous.
"It is the trigger for all the pressures and its workrate is pervasive.
"If for some reason there is a dip, perhaps because of fatigue, maybe some pains and pains, you notice it.
"Some players can escape the game because they carry the ball, Firmino are hard yards all over the country when they are in it.
"For me, this season has not been so intense, and maybe that explains why Klopp did not start him in the mornings to give him this little break.
"Funny, Romelu Lukaku is a similar type that when he falls physically he affects his performances. When he is in it, he is unstoppable.
"The good thing is restoring top fitness is the easiest thing to work for.
"It will be temporary only for Firmino and we have seen in Belgrade, Liverpool is always a better team with him."