Messi is contracted to Barca until 2021 but the six-time Ballons d'Or winner's future is far from certain at Camp Nou, where he has clashed with board members this season.
"I don't think it's a forbidden dream at all. Maybe it wasn't even before this misfortune," he told Radio Rai.
"Messi is at the end of his contract and it would certainly be attempted to bring him home.
"I don't know if this situation will change anything, but I think we will see strange things at the end of the year."
Inter star Lautaro Martinez has been tipped to move to Barca at the end of the season – the Argentina international seen as a long-term replacement for veteran forward Luis Suarez.
Moratti, who was Inter president between 1995 and 2013, suggested Martinez could be used in an exchange deal for countryman Messi.
"He [Martinez] is a very good lad, he cares about his career," Moratti said. "But, as I said before, we have to see if it's part of an operation for bigger players like Messi."