McCullers landed on the DL Sunday, a day after pitching four scoreless innings against the Dodgers in Los Angeles, coming down with what was at first described as right elbow discomfort after he'd thrown 60 pitches.
A quick trip to Houston to see the Astros' doctors proved to be a relief to both the pitcher and the team. The diagnosis was downgraded to a forearm strain.
"It looks like it's muscle only," manager AJ Hinch said. "What that means is that he's not going to throw for a little bit. He's likely not to pitch until September. We do feel like he's going to pitch again.
"We've avoided the major catastrophes that can be when you're talking about elbows and ligaments and issues with the pitcher's arm. I don't have a timetable on when he's going to start throwing, but I know it's going to be a little bit, so he's not likely going to pitch in August but in September, when rosters expand."
McCullers was 10-6 with a 3.93 ERA in 22 starts at the time of the injury.
"The tests came back negative," Hinch said of Springer. "It's simply a sprain of the first knuckle on his thumb. It's not the UCL that a lot of guys around the league have had. We avoided surgery. We avoided a major injury."
• Second baseman Jose Altuve, right knee: He was back in Houston to see team doctors. Hinch said the doctors are happy with the progress he's made and the healing that has taken place. "We'll try to initiate more baseball stuff this weekend when we get back," Hinch said.
• Right-handed pitcher Chris Devenski, hamstring: He's begun a throwing program and has begun to do some baseball-related activities. He could be throwing in the bullpen after the Astros return home following the series against the Giants.
• Shortstop Carlos Correa, lower back soreness: He's played three games for Double-A Corpus Christi. He took Monday off then is scheduled to play nine-inning games back-to-back Tuesday and Wednesday before returning to the Astros this weekend.
• Catcher Brian McCann, knee: For the first time since landing on the DL the first week of July, McCann caught a full bullpen, this one thrown by Justin Verlander. "It's like getting old brothers back together again," Hinch said. "That was the most excited I've seen Verlander to throw a bullpen for quite some time." McCann was able to get into a full squat without discomfort. He still needs to work on agility drills, blocking drills and other catcher-specific work, but Hinch said McCann told him this was the best he'd felt all year.