HOUSTON -- After starting a season-high four consecutive games, Astros catcher Jason Castro was out of the lineup Wednesday. Chris Snyder has been catching Lucas Harrell, who started Wednesday's game against the Padres.

Astros manager Brad Mills said he wanted to get Castro, who missed all of last season after undergoing ACL surgery, into four consecutive games at some point before the All-Star break, but it's no indication of how the playing time will be split going forward.

"I told him we were going to get him up to four times in a row," he said. "I think the way these games set up, being night games and so forth, and now having that extra pitcher in the rotation, it helps out a little bit."

Castro is expected to start Thursday's series finale, with Snyder getting Friday's day game at Wrigley Field.

Mills expects the playing time to be more split as the Astros employ a six-man starting rotation through the All-Star break.

With Bud Norris set to return from the disabled list on Friday, Houston is opting to keep rookie left-hander Dallas Keuchel in the rotation.

Maxwell to miss 4-6 weeks after ankle procedure

HOUSTON -- Astros outfielder Justin Maxwell, who's expected to miss four to six weeks after he undergoes a procedure to remove two loose bodies in his left ankle, will be examined in Houston on Thursday morning by Dr. Kevin Varner, who will perform the procedure.

Maxwell, who has not played in the outfield since June 20 due to lingering discomfort in the ankle, will undergo an arthroscopic procedure within the next week to remove the loose bodies. He has eight home runs and 24 RBIs in 61 games this season, including a Major League-best three pinch-hit homers.

"We'll get it taken care of and I'll be able to play the last half of the season, instead of trying to play through a nagging injury and having surgery in August and wasting time," Maxwell said.

Maxwell hoped to play through the condition, but he was experiencing discomfort after his most recent pinch-hit at-bat on Monday. A cortisone shot took care of some of the symptoms, but not enough to play through the pain.

"It's frustrating, but I need to get it taken care of," Maxwell said.

Altuve nearing return; Lopez out until break

HOUSTON -- Astros manager Brad Mills hopes to have starting second baseman Jose Altuve back in the lineup this weekend in Chicago. Altuve left Sunday's game with a strained right hamstring and hasn't been available, except to bunt if needed.

"We're going to run some further tests today to see how well he's progressing, and hopefully that is good news and we hope to have him back fairly shortly," Mills said before Wednesday's game against the Padres. "He's got to pass all those tests."

Mills doesn't want to put Altuve back on the field until he can run at 100 percent. It's unlikely Altuve would return any earlier than Saturday. The Astros are scheduled to arrive in Chicago at 4 a.m. on Friday morning in advance of a 1:20 p.m. game, and Mills doesn't want Altuve to play without being able to take infield or batting practice. Meanwhile, Mills said relief pitcher Wilton Lopez won't return until after the All-Star break. Lopez, who has been out since June 11 with a sprained right elbow, threw in the bullpen for the first time Wednesday. He's scheduled to throw another bullpen in Chicago and next week in Pittsburgh before starting a rehab stint.

Infielder Marwin Gonzalez, a Rule 5 pick, is scheduled to join Triple-A Oklahoma City on Thursday in Iowa to begin his Minor League rehab stint. He's been out since June 7 with a bruised right heel.