The move was retroactive to Saturday, a day after Blalock was injured against Minnesota. He's hitting .299 with three home runs and seven RBIs.
Texas also designated first baseman Jason Botts for assignment. The 27-year-old switch-hitter made the Opening Day roster for the first time in nine professional seasons but was batting .158 in 15 games, including nine starts. He had 18 strikeouts in 38 at-bats.
The Rangers have 10 days to trade, release or send Botts outright to the minor leagues.
Texas filled the roster spots by recalling outfielder Brandon Boggs from Oklahoma and purchasing the contract of first baseman Chris Shelton from the Triple-A farm team. Boggs hit .309 in 18 games, and Shelton was hitting .354 with three home runs and 18 RBIs.
Manager Ron Washington said Shelton would get most of the playing time that Botts had been splitting with Ben Broussard.
"If he's still swinging the bat, we'll keep him. I'll have Broussard take some fly balls at the [outfield] corners. He'll give me a bat off the bench."
Washington said said Boggs would give him a switch-hitter off the bench if he isn't in the outfield.
"He has some speed, and I can use him as a defensive replacement," Washington said.
Shelton has played in the majors while Boggs has not.
"We just want them to come up and do what they were doing well at Oklahoma," Washington said.