The Dodgers were so concerned about Hong-Chih Kuo last week that they told Ramon Troncoso he would be recalled from triple-A Albuquerque.
They changed their minds, for a few days anyway. But, after Kuo struggled to loosen up on Friday, the Dodgers put him on the disabled list on Saturday and promoted Troncoso to replace him.
The Dodgers said Kuo had a lower back strain, a relatively benign diagnosis for a pitcher who has had four elbow operations.
"The good part is that it isn't the elbow or the shoulder," Manager Don Mattingly said.
Kuo was an All-Star last season, when he posted a 1.20 earned-run average and walked 18 in 60 innings. He has walked four in 22/3 innings this season.
"It's not because of my elbow, my shoulder or my back," he said on Thursday. "I just have to make a pitch."
The Dodgers sent Kuo for an MRI examination last weekend. Kuo has pitched once since then, throwing 15 balls in a 22-pitch outing against the San Francisco Giants on Wednesday.
Mattingly said Kuo struggled to throw strikes while warming up in the bullpen on Friday, prompting the team to put him on the disabled list and order additional tests. Mattingly was unsure what tests Kuo would have.
Kuo was not at Dodger Stadium before Saturday's game. His absence leaves the Dodgers without a left-hander in the bullpen.
Troncoso had a 2.57 ERA in three appearances at Albuquerque.
Garland's first balk
Jon Garland was called for the first balk of his 12-year career on Friday, amid a three-run rally by the St. Louis Cardinals. Garland was cited for what he said was his typical move in the stretch.
"I've been doing that my whole career," Garland said after the game.
On Saturday, Mattingly said the Dodgers would ask Major League Baseball to review the play.
"I'm sure, technically, maybe it's a balk," Mattingly said. "But guys do it all the time. There was no intent to deceive."