The decision was a tough one, but manager Mike Matheny believes the move will give Wacha an opportunity to improve.
"This is an opportunity for him to go down and really establish the bottom of the zone," Matheny said. "We want him to establish the strike zone with his fastball and be working ahead in counts. We want him to continue to work on his breaking ball, but that bottom-of-the-zone fastball is what makes his changeup so good. We want to see him continue to be consistent, and that just comes with repetition. It was time for him to go back and do it."
Wacha's demotion means that fellow rookie Tyler Lyons will start Sunday's series finale against the Marlins. The left-hander, who is 2-2 with a 3.51 ERA over four starts, has impressed Matheny.
"It's nice to have that left-hander in our starting rotation, and it's been nice to watch Tyler do his thing," Matheny said. "He's been very efficient and given us a chance every time he's been out there. Michael did a great job, too, but right now it's a better fit for Tyler to be in there."
Beyond Lyons' success and a desire to see Wacha work on some things, Matheny explained that the decision to option the talented rookie involved managing Wacha's innings.
"We'll have to look over his whole workload," Matheny said. "We don't want to find ourselves in a situation at the end of the year where we have a kid that we can't use because he's had too much work. We're trying to be smart about that and also allow him to work on some things. When he comes back, we'll see how he throws."
David Villavicencio is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.