Sad to say, although he's a proven striker, I think he's not physically built for EPL. He's by far, too short and small in size. Defenders like Campbell and Primus need minimal body contact to nudge Rossi off the ball.
Yes, he did score lots of goals during his loan spell at Parma but Serie A is more on technical plays and not physical ones like the EPL. He did not enjoy a good spell at Newcastle. This proves that Rossi is technically gifted but not well suited for rough treatment of EPL.
Unless he works on his upper body strength, otherwise i see no future for him at United.
Cheers.
CK