MILWAUKEE -- Astros manager Brad Mills is still trying to get a feel for how much of a workload catcher Jason Castro can handle after missing all of last season following major knee surgery. Castro has started 11 of the team's first 17 games.

"We're still feeling our way around on how his knee is going to respond to catching three or four times a week and so forth," Mills said. "We're not 100 percent sure of where we're at yet. We're still talking to the trainers and talking to him after each game and seeing how he feels and how he's moving."

Mills said there has been some concern recently about the number of pitched balls that have been getting past Castro, which could be a product of him still getting back into game shape as well as getting familiar with the pitching staff.

Castro and catching coordinator Matt Sinatro worked on some drills last weekend to address it.

"It was about a week ago we were taking notice of it, and we've talked to him about it," Mills said. "I know what he's coming back from and know what he missed last year with the knee situation. We're getting a bit more familiar with how the knee is going to feel, how it moves, how the pitchers are pitching and so forth."

Mills settling on regular lineup for Astros

MILWAUKEE -- With a good mixture of lefties and righties, speed at the top in Jordan Schafer and one of the team's best hitters in Jose Altuve in the No. 8 hole, Astros manager Brad Mills appears to have settled on a lineup configuration.

When the regulars are starting at the eight positions, the Astros have three left-handed bats in the order in Schafer, Brian Bogusevic and Jason Castro and one switch-hitter in Jed Lowrie, who homered from the left side of the plate in the first inning Monday. It's a good balance, says Mills.

"I think the lineup we have right now with the batting order, we can produce the kind of runs we want to produce," he said. "That's what we try to do is balance this thing out. Altuve is swinging the bat so well in the No. 8 hole, and Jed Lowrie keeps coming around and swinging the bat well. Carlos [Lee] is built for the fourth hole, and J.D. [Martinez] is getting on base and doing things in the third spot."

There has been more uncertainty in the second and eighth spots in the order so far this season, though Mills said last week he prefers to have Lowrie hit second because of his ability to hit left-handed.

Martinez returns to site of big league debut

MILWAUKEE -- The three-game series against the Brewers at Miller Park marked the first trip to Milwaukee for Astros left fielder J.D. Martinez since he made his Major League debut here last July 30. Martinez doubled in his first big league at-bat.

"I said it the moment I got in the taxi taking me here," Martinez said Monday. "I was thinking, 'This is the same taxi ride, except not from the airport this time.' I remember seeing the ballpark from afar and going through the whole day. Everything seems like it's a flashback."

Martinez, of course, established himself pretty quickly by notching 28 RBIs in August and began this season entrenched as the club's No. 3 hitter. As he reflected upon his Miller Park debut, Martinez is much more confident in his surroundings these days.

"I know what to do and I'm not worried about where I have to go, what I have to do," he said. "I'm not overwhelmed. I feel a little more in control of the situation now."