The All-Star first baseman was at Osceola County Stadium early Sunday morning rehabbing the knee, doing simple squats, leg raises and knee bends after having loose cartilage removed from his left knee.
He is expected to miss two to four weeks, but he hopes to be back in his routine in two weeks.
"In two weeks, I'll be able to do pretty much everything, baseball stuff," Berkman said after his therapy session. "I'm not sure they're going to want me to play in a game at that point. But I think two weeks and I should be pretty much back to normal."
Team medical director Dr. David Litner told Berkman on Saturday that he had no ligament or meniscus damage.
Astros manager Brad Mills says the team will be cautious in bringing their star back.
"I want him to be 100 percent," Mills said. "I want him to feel like he's ready to go and that he's gotten enough work, enough at-bats. We'll just see how it goes. We're definitely not going to rush him back."
Sitting the 34-year-old Berkman could be a challenge for the first-year manager.
Berkman tried to talk Mills into playing him in the first game of the spring, when the swelling in his knee first appeared. Mills won out that time, but Berkman will be anxious to bounce back from one of the worst seasons of his career.
And the Astros desperately need his bat in a lineup that lost Miguel Tejada and finished near the bottom of the NL in runs, home runs, RBI and on base percentage.
Berkman posted the lowest batting average of his 11-year career (.274) last season and had just 80 RBIs, though he still had a .399 on base percentage.
"If I'm ready to go, I'm going to run out there regardless," Berkman said. "I've done it before where I had spring training the first month of the season when I had knee surgery the other time. It's not an ideal situation. I'd like to have 50 or 60 at-bats down here this spring and I'm obviously not going to get that. But I don't think it's going to have that big of an impact."
Berkman injured his left knee while running the bases during team workouts earlier this month and missed the spring training opener. He had the knee drained twice, but it continued to swell.
Berkman has had knee problems before. He had arthroscopic surgery on the left knee in 1999 and had surgery following the 2004 season on his right knee after tearing his anterior cruciate ligament.
"Opening Day is great, but it is just a game," Berkman said. "I'm not going to jeopardize two or three weeks of the season if I don't feel like I'm ready to go on Opening Day. I either will be ready on Opening Day or shortly there after."
If Berkman can't play, the Astros will start utility man Geoff Blum at first. He is hitting .471 with four RBIs this spring.