Rossi only made three starts for Newcastle during his loan spell, with another eight appearances as sub.
His best performance was arguably when he scored in the 3-0 win over Portsmouth in the League Cup.
Former Toon Striker Heading To Man Utd?
The Red Devils sold the Italian in 2007 for £6.6million but they insisted a buy-back clause be inserted into the player's contract.
Although the media called him Italian during his spell on Tyneside, he is actually American-born.
Man United travel to Villarreal in the UEFA Champions League group stages on Tuesday,
Ferguson: "He's a good player, in fact, an excellent player. It was difficult to let him go to Villarreal.
"It was based on the fact that he wanted first-team football and we couldn't guarantee him that.
"When they offered the money they did for him and we got the buy-back clause, it became attractive to us.
"We'd consider buying him back. We will keep our options open."