Volquez was scratched from his scheduled start on Sunday. Left-hander Travis Wood will start in his place in the series finale against the Cubs.
"His velocity is there, everything's there," said manager Dusty Baker of Volquez. "We'll have him do some mechanical work on the side with [pitching coach] Bryan [Price]. He needs to get everything back together."
Since making his season debut after returning from Tommy John surgery, Volquez has gone 3-2 with a 6.17 ERA in eight starts. He's walked 27 batters in 35 innings.
"I feel like right now my velocity is good, everything is good," Volquez said. "I just need to find my release point. I don't feel [any pain] in my arm. I feel really good."
While it's common for pitchers coming off Tommy John surgery to initially struggle with their command, the Reds don't have much time to determine their postseason roster by the Sept. 1 deadline.
"It's about who's pitching the best and who can help us the most down the stretch," Baker said.
It's uncertain how or when Volquez will be utilized in relief. Volquez warmed up in the bullpen but was not used in Wednesday's 12-11, 12-inning victory at Washington.
Volquez said he's never pitched in relief in his professional career.
"No, not even in the Minor Leagues," he said.