Aceves had been scheduled to throw 40-45 pitches off a full mound but felt more discomfort in his lower back, which has kept him on the disabled list since May 12. Aceves is being sent to New York to be evaluated by team physician Christopher Ahmad.
"From what I understand, he started his bullpen [session] and wasn't able to finish it," manager Joe Girardi said. "They're going to have to look at every alternative they have to see what's the quickest way to get him right."
This is Aceves' second setback as he attempts to return from the lower back strain, and surgery could now be considered an option. Aceves was 3-0 with a 3.00 ERA in 10 games for New York this year after going 10-1 with a 3.54 ERA in 43 games (one start) in 2009.
"He was extremely valuable for us last year, as anything from a one-inning guy to a three-inning guy that could bridge the gap in a lot of different ways," Girardi said. "People have a chance to step up, and we'll see what happens."