The Italian played for Manchester United 10 years ago, but failed to become a firts-team regular at Old Trafford.
Rossi's career has been hampered by injuries, and made just 42 appearances in three years at Fiorentina.
However, Rossi has a proven track record when he does play and has scored 132 career goals in 323 games.
The striker also has 29 caps for Italy and has scored seven international goals.