HOUSTON -- Astros starting pitcher Joe Musgrove was activated from the disabled list Monday to start against the Rangers, and he will assume the roster spot of Lance McCullers, who was placed on the disabled list with lower back soreness.
McCullers joins lefty ace Dallas Keuchel, Charlie Morton and Collin McHugh on the DL after Astros team doctors diagnosed the righty with lower back soreness on Sunday, sidelining him for his scheduled start on Tuesday vs. the Rangers. McCullers is second on the club in wins, sporting a 6-1 record and a 2.58 ERA this season in 13 starts.
"It's something that would've made him miss his start [Tuesday]," Astros manager A.J. Hinch said. "So then we decided to put him on the DL, give him complete rest and hope that he comes back after those 10 days. … We hope it's a short stint from him."
McCullers' stint is retroactive to Friday, the day after he gave up one earned run in a dominant start at Kansas City. The earliest McCullers could return is June 19 against the A's in Oakland.
In his stead, former reliever Brad Peacock will start Tuesday on three days' rest after throwing three innings and 76 pitches against the Angels on Friday. The Astros' No. 1 overall prospectFrancis Martes will make his first career big league start on Wednesday.
"Of the times to send a guy back out after three days, this is probably the best-case scenario," Hinch said of pushing Peacock up a day. "But we put these guys on four- and five-day schedules for a reason, that is the perfect scenario.
"The decision we had to make was Peacock -- who's done it before as a reliever -- or Martes, who is a young kid and has never done it that I know of. I think the decision was easy, and we think Peacock has the best ability to handle it."
Martes' move to the rotation leaves the Astros' bullpen -- which used four relievers on Sunday -- an arm short, but it keeps the Astros' other starters at normal rest.
Not including McHugh, who hasn't made an appearance in a game in 2017, McCullers, Keuchel and Morton are 20-4 this season in 34 combined starts. The trio has accounted for 223 of the Astros' 647 total strikeouts in 2017.

Fantasy spin | Fred Zinkie (@FredZinkieMLB)
While owners will be hard-pressed to replace McCuller's production (2.58 ERA, 1.06 WHIP, 10.4 K/9 rate), they could use the injury as an opportunity to add a high-upside arm. Atlanta's Sean Newcomb warrants consideration after allowing one unearned run with seven K's across 6 1/3 innings during his big league debut, while Detroit's Buck Farmer is heading into a favorable schedule after tossing 13 scoreless innings across two starts. For some other options, Arizona's Zack Godley (2.44 ERA, 0.99 WHIP) and Tampa Bay's Jacob Faria (12.9 K/9 rate in Triple-A this season) possess exciting long-term potential.