Chapman has failed to consistently hit his usual triple-digit mark in his past two outings and said he's feeling "a little fatigue" in his left arm of late.
"It's been a couple games back, I feel like I haven't been myself," Chapman said. "I felt a lot of fatigue when I go in there, but I don't think it's anything major or [anything] wrong. I just feel weak."
Reds manager Dusty Baker expressed his concern after Monday's outing, when Chapman walked his first two batters on nine pitches in the 10th inning of the Reds' 4-3 14-inning win over the Pirates and was eventually removed in the middle of an inning for the first time this season.
"I was worried more about his command than I was his velocity," Baker said. "I talked to Dr. [Timothy] Kremchek [team doctor], talked to our medical staff and trainers, and they just said he was a bit fatigued. The guy throws 100 mph, he's going to fatigue something sooner or later."
Chapman assured there was no pain in the arm and chalked up his lack of accuracy to the exhaustion. Baker wasn't sure how long Chapman would be off-limits, but the 24-year-old southpaw said he would be ready in "five days to a week."
"No, no, no. No pain at all. It's just fatigued," Chapman said. "It's happened before, but I think it's happened to every pitcher. A majority of other pitchers have had this problem before. It's just dead ... thank God."