Bourn, who suffered a mild right oblique strain Friday, and Manzella, who strained his right quadriceps muscle Saturday, were both held out of drills Sunday. Berkman is a week removed from surgery on his left knee, and he doesn't appear close to returning. Alberto Arias will undergo an MRI on his right shoulder Monday.
What's more, non-roster outfielder Jason Bourgeois left Sunday's game against the Red Sox in Fort Myers, Fla., with a strained left hamstring. His right hamstring had sidelined Bourgeois for a few days early in camp.
Houston general manager Ed Wade said Sunday he remains confident Bourn and Manzella will be ready for the start of the regular season April 5. Bourn is listed as day-to-day and is being held out as a precaution, but Manzella will be out seven to 10 days.
"You go through these types of things," Wade said. "These are resolvable issues. They're not ACLs or a torn quad or a torn oblique. They're strains and sprains and upper-respiratory infections and those types of things. From that standpoint, these are short-term deals one would expect to have happen at different points in Spring Training.
"We just happened to have a couple of them back-to-back. With two weeks left to go -- at this stage we're optimistic they'll all resolve themselves and they'll be ready to go."
Berkman, who underwent surgery March 13 to clean out loose cartilage in his left knee, had to have more fluid drained from his knee Saturday. Until the swelling goes down, Berkman won't be cleared to do any baseball-related drills.
"It's not something that I can say, 'Yeah, it's going to be three or four days from now,'" Berkman said. "I just don't know. I just have to wait and see how it does on a day-to-day basis."
Berkman is still aiming to be ready to play Opening Day, even though Wade remains cautious about saying the slugger will be ready to play in two weeks.
"I'm not going to rule that out for another week to 10 days," Berkman said. "You just don't know how [the knee] is going to respond."
Manzella is expected to miss at least another week after straining his right quadriceps trying to beat out a grounder Saturday. He's going to be held out of baseball activities, and Wade pulled him aside Sunday morning and told him to take it easy.
"I don't need a guy that's going to go out there and gut it out for 10 days of Spring Training and miss a whole bunch of time when the season starts," Wade said. "I'd rather have him discipline himself and take the cautious approach and play 150 games at shortstop. I know how he's wired, so I know he wants to play. The last thing we need is for him to go out there and have the quad roll up and he's out for two months. We don't need that. We need him to just to be honest and take his treatment and when he's ready to go, he's ready to go."
Manzella was still sore Sunday and suffering from some cramping in the area.
"Other than that, it feels pretty positive today," he said. "Right now, with about two weeks left in camp, it's not really a time to hurry up and try to get back out there. If it feels good, I'd like to get out there as soon as possible. I know the training staff, with the season so close and stuff, they're going to want to make sure when I get out there I'm 100 percent. Hopefully that's sooner rather than later."
Arias was diagnosed with a right shoulder strain March 12 and has lost about 5 mph on his fastball while throwing on the side. Wade said Arias threw Saturday and the "results were iffy," which is why the club opted to have a precautionary MRI.
"It's getting better, but I lost some velocity," Arias said. "That's the thing we have to find out."
Meanwhile, right-hander Yorman Bazardo remains sidelined after coming down with shoulder discomfort a week ago. He's throwing on the side and working on range-of-motion activities. Bazardo, who is out of options, was competing for a spot in the starting rotation.
Brian McTaggart is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.