Perez was optioned to Triple-A Fresno on Tuesday, Chandler Rome of the Houston Chronicle reports.
The Astros wanted to bring in a fresh arm for Tuesday's bullpen game, so Perez will swap places with fellow left-hander Framber Valdez. Perez owns a 3.86 ERA and 7:5 K:BB through seven major-league innings this season. He should be back up in early September.