Leiter was optioned to Triple-A Iowa on Saturday, Tim Stebbins of NBC Sports Chicago reports.
Leiter was called up by the Cubs on June 21 but wasn't particularly sharp during his stint with the major-league club. He posted a 4.64 ERA and 1.17 WHIP in 21.1 innings over seven outings during his time in the big leagues and will head back to the minors as part of a move after Steven Brault's contract was selected Saturday.