Jason Castro's homer was a bright spot for the Houston Astros in a 4-2 loss to a Detroit Tigers split squad on Sunday.

However, the injury news for the rest of the team wasn't as positive.

Center fielder Jordan Schafer and shortstop Jed Lowrie remained off the field just five days before the Astros' regular season opener.

The Astros would not dismiss the possibility of one or both players starting the season on the disabled list.

Schafer, who has a sprained left hand, and Lowrie, out with a strained right thumb, were scheduled to bat first and second for Houston.

The Astros wanted to get Schafer a couple of at-bats Sunday for the first time in two weeks, but he experienced pain in his wrist while taking batting practice and told manager Brad Mills he could not swing.

"There's no doubt that the anxiousness mounts each day," Mills said, "because it shortens the at-bats that he's going to get before the season starts."

Lowrie injured his thumb while sliding into second base on Tuesday. He has not played since.

The Astros told Brett Wallace, their opening day first baseman a year ago, that he will be sent down to Triple-A Oklahoma City to start the season as a third baseman.

They also informed Castro, second baseman Jose Altuve, outfielders J.D. Martinez and Brian Bogusevic and shortstop Marwin Gonzalez that they will open the season on the major league roster for the first time.

"It's one of the fun things we get to do," general manager Jeff Luhnow said. "We brought 'em all into Brad's office to let them know. They were all thrilled, as you can imagine."

Gonzalez, a 23-year-old Rule 5 acquisition, can play three infield positions, but Mills called him "a true shortstop" and he might prove to be the Astros' opening day shortstop if Lowrie goes on the DL.

The likely starter in center field, if Schafer can't play, would be Bogusevic.

Castro, hitting .341 in the spring after missing the entire 2011 season due to knee surgery, hit his first spring home run for the Astros' only run off Detroit starter Doug Fister.

Jhonny Peralta hit a two-run homer off Houston starter Wandy Rodriguez, who will pitch the season opener against the Colorado Rockies.

Peralta drove in another run with a double in the sixth inning.