Brantley, whose .315 batting average puts him among the American League leaders, had missed the past three games for the AL West-leading Astros after leaving Saturday's game against the Los Angeles Angels due to soreness in the knee.
"It's not worse, we just didn't think he was going to be ready to be 100% by the weekend," Baker told reporters prior to Wednesday's game vs. Texas. "We're trying to get him back to 100% so we can make this stretch drive and hopefully into the playoffs."
Brantley missed 12 games earlier this season with a sore right hamstring. The veteran left fielder has eight home runs and 45 RBIs this season.