Rossi, who tops the Serie A goalscoring charts with 14 strikes this season, was withdrawn after 71 minutes of Fiorentina's 1-0 win over Livorno on Sunday following a tackle with Leandro Rinaudo.
The Italy international has suffered torn cruciate ligaments in his right knee twice in the last three years, and his club have confirmed that he will undergo further tests on Monday.
"ACF Fiorentina announce that following a challenge from Livorno player Rinaudo, Giuseppe Rossi suffered a sprain to the knee that had already been operated on," the club stated on their website.
"Tomorrow more tests will be performed."
After Sunday's win at the Stadio Artemio Franchi, Fiorentina sit fourth - five points clear of Inter in fifth, with Walter Mazzarri's side due to play Lazio on Monday.
