HOUSTON -- The Astros recalled right-handed relief pitcher Enerio Del Rosario from Triple-A Oklahoma City on Monday to take the roster spot that opened up when right-handed starter Jordan Lyles was optioned back down after starting Sunday's game against the Rangers.

The Astros will carry eight relief pitchers for the next week and will go with a four-man rotation. They won't need a fifth starter until Monday's doubleheader in Colorado, at which time a new rule will permit them to expand their roster to 26 players for one day.

Houston manager Brad Mills said that roster spot will be occupied by another starter. That could be Lyles, who wouldn't have to stay in the Minors for the usually required 10 days under that scenario. Mills said the rotation at Oklahoma City could be tweaked so Lyles would be in line to start one of the games Monday.

"Monday won't be his regular day to start, so we could adjust some things at the Minor Leagues in Oklahoma City to make that available, and we'll proceed with that," Mills said. "For us, [the 26th player] is probably going to be the starter for that game."

Galarraga signs Minor League deal with Astros

HOUSTON -- Armando Galarraga, the pitcher who was denied a perfect game two years ago when umpire Jim Joyce missed a call at first base that would have been the final out, has signed a Minor League contract with the Astros, general manager Jeff Luhnow said Monday.

Galarraga, 30, will help the Astros fill a rotation spot at Triple-A Oklahoma City, which has a need for a starter after Henry Sosa agreed to pitch in Korea. Galarraga has appeared in 95 career Major League games with the Rangers, Tigers and Diamondbacks, going 26-39 with a 4.69 ERA. He was released by the Orioles in April.

Luhnow said Galarraga will throw a couple of bullpen sessions in Kissimmee, Fla., before joining the RedHawks.

"We've got to watch him throw," Luhnow said. "I think [Tuesday] he's scheduled to throw for the first time, and if that goes well, he'll face some hitters and then go out and pitch."

On June 2, 2010, Galarraga pitched 8 2/3 perfect innings against the Indians and appeared to record the 27th consecutive out when Jason Donald hit a ground ball to first baseman Miguel Cabrera, who flipped the ball to Galarraga covering first. Joyce incorrectly called Donald safe, costing Galarraga a perfect game. He settled for a one-hitter.

Joyce later apologized to Galarraga for missing the call.

Galarraga went 4-9 with a 4.49 ERA in 25 games (24 starts) for the Tigers in 2010, winning only two starts following his near-perfect game. He was eventually traded to the D-backs and went 3-4 with a 5.91 ERA in eight starts.

Schafer ready to return to on-field action

HOUSTON -- The lower leg muscle strain that kept Astros center fielder Jordan Schafer out of Sunday's game against the Rangers had improved so much Monday he was available to play, but he wasn't in the starting lineup for the opener against the Cubs.

Schafer, who sustained the injury in the third inning of Saturday's game against the Rangers, said he sent a text to head athletic trainer Nate Lucero around noon Monday informing him he was ready to go. Alas, Brian Bogusevic started in center field.

"Everything was fine," Schafer said. "I can play tonight. I don't make up the lineup, but whatever [manager Brad Mills] wants to do. I can play tonight, though."

Mills said Schafer would be available to pinch-hit and pinch-run, unlike Sunday when he couldn't play. The Astros were short-handed on the bench Sunday and sent starting pitcher J.A. Happ to pinch-hit in the fifth inning of the loss to the Rangers.

"That's real good news and will help fill out our bench," Mills said. "[Sunday] we felt short-handed not having him."

Buck gets a shot to hit third in lineup

HOUSTON -- Outfielder Travis Buck became the fourth different player to occupy the No. 3 spot in Astros manager Brad Mills' lineup in the past four games, starting in right field Monday against the Cubs.

J.D. Martinez, who's hit third for much of the season but is mired in a slump, hit third on Friday, with Justin Maxwell batting third Saturday and Brian Bogusevic on Sunday. Mills perferred Buck on Monday because he had experience against Cubs starter Matt Garza.

"I want a guy that can put the bat on the ball and put it in play and maybe we can do some things," Mills said. "I'm not saying we can't do that with Bogie, because he brings speed and power to the table. Maybe just a different look is what we're looking for."

Buck, making his 15th start of the season, said hitting third doesn't come with a different approach.

"Hitting in front of Carlos [Lee], I'm going to see a lot more strikes, but I've always got to make sure they're pitches I can put in play and put some good swings on because I have a couple of guys ahead of me [Jose Altuve, Jed Lowrie] who are a little fast," Buck said. "I'll be able to live with the single, rather than somebody needing an extra-base hit to score. I'll be able to take advantage of hitting singles rather than looking for a pitch to drive in the gap."