Trio released by Manchester City
All three players were out of contract at Eastlands and have been on the fringes of the first team since Mancini took charge in December.
Bulgarian international winger Petrov, 31, managed 57 starts after an injury-plagued three years at the club, while Zimbabwe captain Benjani ended last season on loan at Sunderland after falling down the pecking order at City.
Veteran Brazil defender and former Champions League winner Sylvinho leaves after joining from Barcelona at the start of last season.
City signed Hamburg SV's German international defender Jerome Boateng last week.