"It's very disheartening," Reds manager Dusty Baker said. "I know he was so close to being himself. He's worked hard. I just hope we can come up with a solution."
Cueto felt pain when he threw a 1-2 pitch to the Rangers' Mitch Moreland during the Reds' 4-0 loss. He immediately exited the game.
"Your heart sort of sinks when you go out there when you know the news you're about to get," Baker said. "You could see the look on his face. Especially for a guy that loves to pitch like Johnny. He lives for it."
Cueto is 4-2 with a 3.33 ERA in nine starts. He was out from April 15-May 20 with a strained right lat muscle. His second DL stint lasted from June 5-16 because of a right shoulder strain.
Left-hander Tony Cingrani, who replaced Cueto on Friday and during both of his stints on the DL, will move back into the rotation. Cueto's next turn in the rotation was expected to be Wednesday against the Giants.
Ondrusek was 2-0 with a 5.64 ERA in 21 appearances for the Reds during his previous callup from Double-A Pensacola from April 10-June 8. At Louisville, he had six scoreless relief appearances totaling eight innings, with four hits, two walks and six strikeouts.
"It's been going all right," Ondrusek said. "I'm throwing the ball well and trying to stay as consistent as possible."
Ondrusek, who last pitched on Thursday for the Bats, flew to Texas on Saturday morning. He was expected to be a main cog in the bullpen, but his struggles in the Majors have traced back to late last season.
"They made the decision that I need to go down there [to the Minors] and get some more work," Ondrusek said. "I need to go out there, keep getting people out and show the consistency that is needed to get back here as quick as possible."
Mark Sheldon is a reporter for MLB.com. Read his blog, Mark My Word, and follow him on Twitter @m_sheldon. This story was not subject to the approval of Major League Baseball or its clubs.