The 27-year-old Portuguese international is expected to touch down in Milan tomorrow to undergo a medical.
"It will be a loan," Tirri told FC Inter News. "I think that the buy-out option will be set at around €4m-€5m (£3.4m-£4.3m).
"The credit for the move goes to Inter technical director Marco Branca. He's the man responsible for this deal. His relationship with Porto president Pinto da Costa proved to be the difference."
Rolando, who spent the latter half of last season on loan at Napoli, will be reunited with coach Walter Mazzarri.