Houston purchased veteran left-hander Raul Valdes' contract from Triple-A Oklahoma City and optioned Chapman to the RedHawks on Thursday.
Chapman had struggled with command in 3 2/3 innings of five-run work this season, including seven walks. He walked the only batter he faced in Wednesday's 6-4 loss to the Royals, part of Kansas City's two-run seventh inning that tied the game and led to extra innings.
"It's really hard when you talk about pitching out of a bullpen, because you have to throw strikes all the time," said manager Bo Porter. "You're usually coming into a situation with men on the base, the last thing you can have is a free pass. There's no defense for it.
"At least if the guy throws strikes and forces a guy to swing the bat, we have an opportunity to defend. That's the message we delivered to Chapman after the game. We told him he has the stuff to pitch here, but you have to command it."
Valdes is playing in the big leagues for his fifth team, after previous stints with the Cardinals, Mets, Phillies and Yankees produced a 4.94 ERA and a 7-7 record.
He'd already earned a pair of saves for Oklahoma City, tallied a win in Wednesday's game and went 2-0 with a 1.69 ERA in five-plus innings of Spring Training with the Astros.
"He's a veteran guy who's been in this role before," Porter said. "At this juncture, we need the ball put in play or a strikeout from our bullpen. [Valdes] is more experienced in the role, and probably gives us a little bit more as far as usage and innings goes."
Valdes' plane didn't even arrive in Houston until 4:15 p.m. CT, meaning he didn't reach the ballpark until about 90 minutes prior to Thursday night's game against Kansas City. Porter said he would still be available to pitch against the Royals.
Chris Abshire is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.