Lyles, 22, struggled this spring, allowing 36 hits and 23 earned runs in 11 2/3 innings.
"I need to focus on pitching downhill more and attacking the bottom of the strike zone," Lyles said following the move.
General manager Jeff Luhnow said that the organization is confident Lyles will get on track and be in the rotation for years to come. Lyles was the youngest starter in the National League for most of his four stints in Houston last year, going 5-1 with a 5.09 ERA in 25 starts.
"Lyles is going to be a part of our organization for a while," Luhnow said. "He knows that. I know it's frustrating and disappointing for him to have to go back to Triple-A. Last year I agonized about that conversation, and yet a month later he was back in Houston. He's clearly a Major League pitcher."
While Lyles has been working on several mechanical issues this spring, Luhnow said it's a matter of effectiveness.
"He's been around the zone, which is good, but his pitches are getting hit," Luhnow said. "So for whatever reason, whether it's hitters are seeing him better and [him] telegraphing what he's going to throw, whatever, he's got to get past that, because we don't want him to go to Houston and have the same result early in the season."
With Lyles out of the picture and Bud Norris getting the nod for Opening Day, the Astros tabbed Lucas Harrell as their No. 2 starter and Philip Humber as the No. 3. That leaves right-handers Brad Peacock, Alex White and Edgar Gonzalez, and left-hander Erik Bedard battling for the final two spots.
"Philip Humber has pitched well this spring, and he's an experienced guy," Luhnow said. "We brought in guys like Humber and White and Bedard ... because we wanted to add more experience to the rotation, but Jordan Lyles is 22 years old, and we believe he's going to be a part of our rotation for many years to come."
Brian McTaggart is reporter for MLB.com and writes an MLBlog, Tag's Lines. Follow @brianmctaggart on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.