Petz is replacing Julio Paulino, who withdrew from the fight for yet-undisclosed reasons.
The fight has been verbally agreed to, though Petz has yet to sign a formal bout agreement, according to sources close to the fight.
Petz, who most recently competed in the Moosin pay-per-view show, defeating Ralph Johnson by decision, competed in the UFC five times from August 2006 to October 2007, compiling a 2-3 record.
"The Meat Cleaver" captured victories against Luigi Fioravanti and Sam Morgan during his earlier run, while dropping matches to Marcus Davis, Josh Burkman and Kuniyoshi Hironaka.
Petz has won four straight bouts in pushing his career record to 18-7.
Roberts is 9-1 in his MMA career, losing his UFC debut by KO to John Howard in March.
UFC 116 takes place on July 3 from the MGM Grand Garden Arena in Las Vegas. The event is headlined by a UFC heavyweight title matchup between Brock Lesnar and Shane Carwin.