The Paraguayan international had refused to sign a new deal at the Nou Camp.
The 17-year-old is yet to make his full debut for Barcelona, having joined their youth set-up in 2009 - but he has now opted to move to Italy.
"Roma already put the necessary money to the Spanish Federation for the clause asked by Barcelona", Sanabria told Radio Monumental 1080 AM.
Sanabria revealed that he will not link-up with Roma's first team until next summer as he is set to join another club on loan.
"I'll go on loan to another Serie A team," he added.