Eyre, who made three relief appearances in April after opening the season on the disabled list with a groin injury, had been out since April 22 after having a recurrence of the injury.
"We needed another arm down there," manager Ron Washington said. "Willie can give us two innings."
The Rangers have used closer C.J. Wilson and setup man Frankie Francisco in back-to-back games entering Friday. Another mainstay on the bullpen, Jason Jennings, threw 25 pitches to earn his first career save in Thursday's 9-8 12-inning win at Arizona.
To make room for Eyre, the Rangers optioned outfielder Brandon Boggs to Triple-A Oklahoma City. The Rangers also had to make room for Eyre on the 40-man roster, so they placed infielder German Duran on release waivers for the purpose of giving him his unconditional release.
Boggs was 1-for-17 since being called up from Triple-A on June 2. Duran was batting .149 in 25 games for the RedHawks and had been on the disabled list since June 5 with rib-cage soreness.
Eyre gives the Rangers an eight-man bullpen, something Washington said isn't in the team's long-term plans. The Rangers' bullpen has allowed five runs in the past six innings. Rangers relievers have gone four or more innings in six of the past 12 games and nine times in June after doing so just seven times in April and May.
"We just need to make it through the weekend before we straighten this bullpen out," Washington said. "We'll figure it out this weekend."
Todd Wills is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.