The right-hander has been sidelined during spring training because of the elbow. He was expected to make his first appearance on Monday, but he was sore after throwing a bullpen session. DeSclafani was sent back to Cincinnati on Sunday for an MRI and further examination.
"After the doctors examine him, we'll have a better idea of whether this is a minor or major setback," general manager Dick Williams said.
DeSclafani was in line to start Opening Day last season before he strained an oblique late during camp. He missed the first two months of the season as the injury lingered. He wound up making 20 starts and going 9-5 with a 3.28 ERA.
He was ready to start the season opener this season until his elbow became sore early in camp. He got treatment and hasn't pitched in a game. DeSclafani threw in the bullpen on Friday, getting ready to start a game three days later, but the soreness returned, prompting the Reds to send him back to Cincinnati for more tests.
"He felt a little different than he did previously," Williams said. "There was more cause for concern."
The latest setback makes it likely that he'll have to start the season on the disabled list for the second straight year. The opener is only three weeks away.
It also marks the second year in a row that Cincinnati is trying to cobble together a rotation because of injuries. Homer Bailey had surgery to remove bone spurs from his right elbow last month and is expected to be sidelined for a couple of months. Also, the Reds traded starter Dan Straily to the Marlins in January.
They signed Scott Feldman to a one-year deal, giving him a chance to fill one of the rotation spots. In addition, they're giving Bronson Arroyo, 40, a chance to show he can still pitch. Arroyo, who signed a minor league deal, is trying to come back from Tommy John surgery more than two years ago.
Arroyo came down with the flu early in camp. He made his first spring training appearance on Sunday and pitched two innings against Milwaukee, retiring six of the seven batters he faced, fanning two.
"Today was as good as I could hope for, all the way around," Arroyo said.