HOUSTON -- First baseman Lance Berkman said he's still working his lower body into shape after missing the first 12 games of the season while recovering from arthroscopic knee surgery in March.

Berkman sat out Friday's game in Atlanta with discomfort in his left groin, which was the first game he had missed since he returned to action. Berkman said Monday he still felt some discomfort in the groin, but he was more than able to continue playing.

"It's just the result of I didn't run for five weeks because of my knee, and my legs are not in shape and I had to play nine out of 10 days going as hard as I can. And I think it was my body's way of saying, 'Hey, ease back a lit bit.' I'll monitor it and get treatment on it. I think that the off-day did a world of good."

Meanwhile, right-hander Sammy Gervacio threw a bullpen session Monday to pitching coach Brad Arnsberg and deemed himself available for action. Gervacio left Saturday's game in Atlanta due to a strained right shoulder.

"He says he feels great," Astros manager Brad Mills said. "He feels fine and he's ready to go. We're happy about that."

Slumping Pence gets a day off

HOUSTON -- Right fielder Hunter Pence, who's in an 0-for-9 slump that has seen his average plummet to .213, was out of manager Brad Mills' starting lineup for Monday's game against Arizona. Cory Sullivan started in his place.

"I'm a team player and I'm here to do what's best for the team," Pence said. "Millsie is our leader and we've got to get some of these other guys fresh and give them opportunities, and I try to make the best out of anything that happens.

"I'm going to be ready to play if they need me tonight. I'm going to be ready every day, and I love to play this game and I'm grateful for the opportunity every day to come out here and play. This is some adversity we're facing. No one believes in us, but we believe in ourselves and I believe in us. I'm going to go out there and play the game as hard as I can."

And that hard-nosed attitude is why Pence sometimes needs a day, Mills said.

"He plays the game so hard, and we all see that," Mills said. "He plays the outfield hard, runs the bases hard and hits hard. You want those types of guys on your club, but at the same time, it does take a lot of toll day in and day out with your body."

Johnson takes batting practice

HOUSTON -- Third baseman Chris Johnson took batting practice on the field Monday for the first time since going on the disabled list April 20 with a right intercostal strain. Johnson experienced some pain swinging off the tee in Atlanta last weekend.

"I had some soreness after we hit, so I backed it down and didn't hit," Johnson said. "Today, I got back after it and I'll see how it responds. That's basically what it's coming down to, is how it responds to me taking full swings."

Astros general manager Ed Wade said Johnson will be sent out on a Minor League rehab assignment before being activated.

"He's almost to the point where he might be starting Spring Training all over again because he's missed so much time at this point," Wade said. "He's making good progress and [head athletic trainer] Nate Lucero and the coaches are monitoring it, and hopefully we get him on a rehab assignment sooner rather than later."