The former Liverpool midfielder rates the summer signing from Hoffenheim highly.
Firmino scored his first goal for the Reds during Saturday's remarkable 4-1 win over Manchester City, where he and Philippe Coutinho took the City defence apart to give Jurgen Klopp's side a memorable victory.
Hamann said he spoke to his former teammate Markus Babbel who managed Firmino for a spell at Hoffenheim and commented on what he saw from his time in the Bundesliga.
The former midfielder told the official Liverpool website: "He’s very direct, he’s a little bit different to Coutinho, that’s why he can also play that role as a false nine or a centre-forward.
"Sometimes when Brazilians or South Americans come to the Premier League [people] ask if they can cope with the physical demands but I think he’s more German or European than South American, mentally.
"He never shirked a challenge in Germany, he was always one of the first ones to go where it hurts, and I think he’s shown that in his few games for the club.
"He’s got tremendous ability and, coupled with the mental strength he’s got, I think he could be a great asset for the club for a long time to come."
Firmino looks as if he's not had a problem settling into life in the Premier League and seems to relish the physical aspect of the league. His technical ability and willingness to link others into the game, as well as chase down any kind of ball that could be seen as a lost cause is also commendable, and seems to be endearing him to the club's supporters.
Certainly so far he has shown himself to be versatile in both supporting a main striker and leading the line. Under Jurgen Klopp he seems to have thrived, and the former Borussia Dortmund boss watching him closely in the Bundesliga seems to have had a positive effect, and he now gives Liverpool a good option.