Collins was optioned to Triple-A Iowa on Monday.
Collins was recalled by the Cubs on May 25 but his stint with the major-league squad was short-lived. He appeared in Sunday's contest, allowing one earned run on two hits across 1.1 innings of work. He's pitched well at Triple-A previously this season, producing a 2.25 ERA and 0.92 WHIP with 14 strikeouts across 12 frames.