Firmino missed Liverpool's last three Premier League matches due to a thigh injury.
But the Brazil international was able to take part in the first session of the squad's pre-final training camp on Tuesday, putting him in the running to face Tottenham in Madrid on June 1.
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Firmino was the first player to arrive on the south coast of Spain for some individual sessions with strength and rehabilitation staff.
Having fallen just short in the Premier League title race, Jurgen Klopp's 26-man group are spending six days in Marbella before returning to England to finalise preparations for their attempt to win Liverpool's sixth European Cup.
"Roberto Firmino today trained alongside his teammates following a muscle strain that ruled him out of Liverpool's last three matches," a statement on Liverpool's website revealed.
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"The Brazilian took part in the Reds' first session of their Marbella training camp on Tuesday morning as he works his way back to full fitness.
"Firmino has been working with the club's medical staff on his rehabilitation from the issue and his reintroduction into full team training will be carefully managed under their supervision, with specialised programmes planned over the coming days."
Also included in Liverpool's group is Guinea midfielder Naby Keita, who continues his rehabilitation from a serious groin problem suffered almost three weeks ago.
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