Chapman is battling fatigue in his left arm, which began to bother him two outings ago.
"I feel a lot better," he said. "I think a few more days, I'll be good."
On Monday, he walked two batters on nine pitches before being removed in the middle of the inning. Chapman allowed four hits, including Matt Dominguez's three-run homer, in last Friday's loss to the Astros.
The 24-year-old southpaw said that he has felt this two or three times before in his career, the last of which came in 2011. He is 17 2/3 innings over his career high in innings pitched.
"There's a long season and sometimes you forget about continuing to do some exercises and you get fatigued," Chapman said.
Through 64 games, Chapman is 5-5 with a 1.60 ERA and 119 strikeouts in 67 2/3 innings. His 35 saves are tied with Atlanta's Craig Kimbrel for the National League lead.
"I wish this would've happened earlier in the season, because this is the time of the season when we're on the final [stretch] of the season and I would like to be better," Chapman said.