The Italy international suffered another cruciate knee ligament injury in January, which put his participation in the upcoming FIFA World Cup in doubt.
However, the former Villarreal man played a late cameo during Fiorentina's Coppa Italia defeat against Napoli on Saturday, before coming off the bench to score in the 4-3 loss to Sassuolo three days later.
While Rossi's goal proved to be in vain on Tuesday, Montella was delighted to see his leading scorer back doing what he does best.
"He is an extraordinary player," Montella told Sky Sport Italia.
"(Even) when he's not in great shape he still manages to find that moment of magic from a champion."
Fourth-placed Fiorentina remain on course for UEFA Europa League football next season despite their defeat to struggling Sassuolo and Montella reiterated his desire to see the club strengthen over the close-season.
"I want a team that is reinforced next season, even if it’s difficult to repeat certain results," he added.
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