The 26-year-old's career had ground to a halt after he twice ruptured the anterior cruciate ligament in his right knee while at Villarreal, but the striker has regained form and fitness to top the Serie A scoring charts so far this season.
The former Manchester United youngster has already struck 11 goals in just 12 league appearances for the Viola, and was also on target in Italy's 2-2 draw with Nigeria on Monday.
"I really can't think of a better player in Serie A than Rossi right now," Montella told La Repubblica.
The 39-year-old former Roma boss was equally complimentary towards Rossi's strike partner Mario Gomez, admitting he has been amazed by his worth ethic within the side.
"Men like him can change your life," Montella added. "Against Genoa we were 4-2 up with a few minutes to go, we were struggling and Mario went back to defend.
"I knew he was a strong attacker, but in that moment I understood he was an extraordinary player."