"We needed the extra arm right now," manager Jeff Banister said.
• Depleted 'pen costs Rangers on Saturday
Banister said Martinez is also available out of the bullpen as of Sunday. Martinez threw 75 pitches in his start against the Astros on Thursday, but was bumped out of the rotation when the Rangers acquired Miguel Gonzalez. Martinez will be used in late innings and short relief, Banister said.
Kela has not pitched since Aug. 3 because of soreness in his right shoulder, but he is making progress. He threw off a mound on Friday without issue and will do so again on Monday.
"[Friday] went pretty good," pitching coach Doug Brocail said. "The way he is getting down the mound, the arm angle is good, he's getting closer. He still has to build up strength, but he looks good."
Kela will likely have two more bullpen sessions, including the one on Monday, before he is an option. But the Rangers are hoping to have him back in the next seven days. He is well ahead of Matt Bush, who is sidelined with a sprained right knee. Bush is keeping his arm going by throwing off flat ground, but he is not ready throw off the mound.
Gardewine is the fourth rookie in the Rangers' bullpen, along with Jose Leclerc, Ricardo Rodriguez and Austin Bibens-Dirkx. Gardewine spent the season at Double-A Frisco and was 1-2 with a 2.21 ERA and six saves in 33 appearances. He struck out 13.01 batters per nine innings. He allowed three unearned runs in his only Major League appearance against the Angels, on Aug. 22, when an error by Elvis Andrus set up a three-run home run.
"One outing ... good arm, like the stuff," Banister said. "Need to get him back out there and see mentally how he lets his stuff play."
Rangers relievers have had a blown save in the first two games of the Angels series. Prior to that, they had gone 62 games without a blown save, the second-longest streak in club history.
• Rangers batters have been hit by a pitch 74 times on the season, two short of the club record set in 2015.
• Carlos Gomez was hit by another pitch on Saturday night, extending his club record to 18 and tying Angels catcher Martin Maldonado for the most in the American League. He has 13 since the All-Star break.
• Banister officially confirmed that Gonzalez will start on Tuesday in Atlanta.