HOUSTON -- One day after having his knee drained for the fifth time and getting a cortisone shot, Astros first baseman Lance Berkman said Tuesday he wasn't sure when he would be able to return to the lineup. Berkman, who had arthroscopic surgery on his left knee March 13, is eligible to come off the disabled list Saturday.

"My wife asked me that today and I think she's tired of me moping around the house," Berkman said. "I have no idea [when I'll return]. I really wish I could tell you an accurate prediction of when I thought I would be ready to go. It isn't right this second, but I'm hopeful it will be soon."

The good news for Berkman was his left knee swelled only slightly Tuesday, enabling him to play light catch on the field.

"The last four times I had it done, it swelled right back up, but this time it stayed down a little bit and some of that has to do with the fact they included a cortisone injection with that and that keeps it from swelling," he said. "It feels better today than it has."

Johnson gets first start at third base

HOUSTON -- Facing a left-hander for the first time this season, the Astros had Chris Johnson starting at third base and Jeff Keppinger at second base for the first time this season against Barry Zito and the Giants on Tuesday.

Johnson, who led the Majors with eight home runs in Spring Training, batted sixth in manager Brad Mills' lineup. Pedro Feliz started at first base for the first time since 2007, with Geoff Blum out of the lineup after starting at first on Opening Day.

"I'm sure I will [have butterflies] once the game starts and we run out there, but I'm sure when the first pitch goes it's just another game," said Johnson, who started five games last year at third base in his Major League debut.

Johnson figures to be busy with Astros left-hander Wandy Rodriguez, a ground-ball pitcher, on the mound and facing a predominantly right-handed Giants lineup.

"I think so, especially with his curveball," Johnson said. "He tends to get some guys to roll over the ball, so that's why I'm out there. Hopefully I get some ground balls."

Mills was eager for Johnson to get a chance to get some at-bats after his hot spring.

"Chris had such a good Spring Training that we want to try to get him in there," he said. "That's the biggest thing, whether he's right- or left-handed -- yeah, a little bit because he's right-handed -- but at the same time we're going to try to catch onto something while he's still hot."

Mills adjusts dugout setup

HOUSTON -- Manager Brad Mills had the Astros make some alterations to the home dugout along the first-base line at Minute Maid Park to give him better visual access to the field and better physical access to the players.

Mills had a portion of the protective screen in front of the dugout removed, enabling him to see the field better. Instead of standing at the end of the dugout nearest home plate, Mills is standing on the opposite side of the dugout stairs, closer to the middle of the dugout.

"Everybody likes something different," he said. "I'm not saying one thing is right and another is wrong. The reason I wanted to be on this side of the stairs is I felt I'd have to cross over the stairs ... if I wanted to go talk to the players as they were trying to walk up the stairs to get to the on-deck circle, and this allowed me to not have to do that.

"I'm right here by the bat rack and the stairs, and when a guy goes out on the on-deck circle and I wanted to go down and give him a high five for a getting a sac fly or an RBI ground ball, I can talk to him. I'm not fighting through guys to get down and do that."

Astros veteran Geoff Blum appreciated the gesture.

"I think it's great," he said. "I think the manager should be accessible during the game. He's got the kind of energy you want to feed off of. Last night's game, he was upbeat the whole time and he didn't get down and was talking to guys about pitches that are getting thrown and situations and cheering us the whole way. It was kind of nice to have him involved."

Astros infielders get extra work

HOUSTON -- The Astros have put their infielders through extra drills prior to batting practice, a move suggested by manager Brad Mills so the fielders won't have to worry about taking ground balls during batting practice.

"We try to give our infielders some ground balls without having to dodge BP balls," Mills said.

While Mills was bench coach of the Red Sox in 2005, infielder Alex Gonzalez began taking ground balls early and the other infielders soon followed him. Jeff Keppinger, Tommy Manzella, Chris Johnson, Kaz Matsui and Geoff Blum took part Tuesday.

"We talked to our infielders in Spring Training, and they said, 'Sure', we'd love to do that,'" Mills said. "This enables them to concentrate on some things without balls whizzing by their heads or jumping out of the way of balls."

Worth noting

HOUSTON -- Astros general manager Ed Wade said disabled right-handers Alberto Arias (right rotator cuff impingement) and Yorman Bazardo (shoulder strain) are headed to extended spring training in Kissimmee, Fla., on Wednesday to continue their throwing programs.