To fill Thornton's roster spot, right-hander Pedro Beato was recalled from Triple-A Pawtucket and was active for Wednesday night's game in Houston.
Red Sox manager John Farrell said placing Thornton on the DL was not something the team wanted to do, but had to out of necessity.
"When you get into the oblique injury, even though he feels improved from the time on Sunday when he first suffered the injury, this is something that we don't feel like we want to rush with the potential of any kind of setback," Farrell said. "The fact is, we also needed another arm in here after last night's bullpen use."
Thornton suffered the injury Aug. 4 against the Arizona Diamondbacks, when he threw just six pitches before being removed. Since joining Boston on July 13 in a trade with the Chicago White Sox, he has gone 0-1 with a 2.16 ERA in 8 1/3 innings over 10 appearances.
"I don't want to go to the disabled list -- it's something I despise," Thornton said on Tuesday. "But at the same time, the team comes first, and they have to make a decision."
Beato rejoins the Red Sox for his fourth major league stint of the year. In his nine games for Boston in 2013, he has gone 1-1 with a 3.12 ERA and four strikeouts in 8 2/3 innings.
Steven Wright, who struggled to control his knuckleball in indoor Minute Maid Park and lasted only one inning on Tuesday in his first career start, will move back to the bullpen, primarily as a long reliever, Farrell said.
Farrell was optimistic about what he saw from reliever Rubby De La Rosa in his Red Sox debut on Tuesday night. De La Rosa retired the side in the ninth inning, striking out two, in the 15-10 victory.
"In shorter stints, he does a great job of channeling the adrenaline," Farrell said. "With that kind of power, it was very encouraging."
Farrell didn't rule out De La Rosa's availability for Wednesday night's game. He also mentioned the possibility of De La Rosa's role expanding in the near future.
"Staying consistent with what we've done with other guys, as they pitch and gain confidence, their responsibility will grow," Farrell said.
Information from ESPNBoston.com contributor Jordan Godwin was used in this report.