"Mat threw his bullpen [on Sunday] and had some irritation in his elbow," Reds manager Bryan Price said. "He had some inflammation and tenderness there in the elbow and he wasn't able to get through to the point where he could pitch. We're taking the conservative route to reschedule once we get that soreness out of there."
Latos did not appear in any big league Spring Training games but pitched three times in Minor League games in Arizona. He already made one rehab start with Double-A Pensacola on Thursday and allowed five runs -- three earned -- on seven hits with one home run over four innings.
After the game, Latos told reporters he felt no pain in his knee or elbow. Price said the elbow soreness developed in the following days since.
"That's when Mat has been feeling a little bit of that soreness since he had the elbow surgery, it's been the day after or the first two days after he throws in a game," Price said. "But it's been something he's been able to work through and throw a productive side day and be ready to make his next start. This is the first time I think that we've had an issue where the soreness did not dissipate."
There has been no specific timetable given on when Latos could resume pitching. The Louisville game was expected to be his final Minor League outing before being activated sometime next week. The delay means that Alfredo Simon will get more opportunities in the rotation. Simon allowed one run and four over seven innings on Sunday vs. the Mets.
Price was confident that the setback to Latos was minor and optimistic it would not require another procedure.
"There's nothing that's been suggested that would represent it as serious as far as missing several starts or anything of that nature," Price said. "In the next couple of days, we should know a lot more."
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.