This is really sad news—he had such a promising career derailed by injuries at Villarreal, recovered to show brilliance briefly in Florence before being injured again, and had just recently scored a hat-trick for Celta—his first in La Liga.
According to transfermarkt, Rossi’s contract at Fiorentina ends this summer; they loaned him to Celta last fall and apparently there is an option to extend his contract and loan for the 2017-18 season. Since Rossi won’t be able to return to action for at least six months, perhaps longer, that might not happen.
Rossi turned 30 in February. We wish him all the best and a speedy recovery.