Miller, who is coming back from arthroscopic surgery on his shoulder in late September, made his third rehab start on Monday for Class A Peoria.
"My arm doesn't hurt," Miller said Wednesday. "It's just a matter of the ball isn't coming out of my hands real good right now.
"I've got to find a way out, and how it's going to work," he said. "I haven't figured it out yet. My arm just feels fatigued right now and hopefully a little rest will help."
He will have a throwing session in the bullpen this weekend in Milwaukee, and hopes to make another rehab start for Peoria after the break. His velocity has increased each outing but Miller said, "It's just not where I need to be."
He still expects to pitch this season for the Cubs.
"I hope so," Miller said. "I'm trying right now, and we'll see where it goes."
Extra bases: Mark Prior's left ankle was still sore Wednesday after fouling a ball off it in the second inning on Tuesday. ... The Cubs are 9-20 against left-handed starters and will face three in the next four games in Milwaukee. ... Sean Marshall's start on Wednesday was the 31st by a rookie pitcher for the Cubs. Before this season, rookies made 18 starts over the last three seasons.
Minor matters: Angel Guzman gave up one hit over three shutout innings and struck out four in Iowa's 6-1 win over New Orleans on Tuesday. Casey McGehee had two hits and three RBIs. Michael Restovich hit a solo homer. ... Nic Jackson had three hits and one RBI in West Tenn's 10-4 loss to Chattanooga. Brian Dopirak had two hits and an RBI, and Bobby Brownlie gave up eight runs on 11 hits over three innings. ... Donald Veal struck out six over seven scoreless innings in Daytona's 3-0 win over Brevard County. Grant Johnson picked up his first save, pitching two scoreless innings. Jemel Spearman and Matthew Ciaramella both had two hits. ... Mitch Atkins gave up five hits over six scoreless innings in Peoria's 6-2 win over Clinton. Yusuf Carter, Kyle Reynolds and Dylan Johnston each had two hits. ... William Muldowney gave up three runs, one earned, on seven hits and struck out six over five innings in Boise's 7-5 win over Yakima. Sammy Baez and Elvin Puello each had two hits.
On deck: Veteran Greg Maddux will open the Cubs' four-game series against Milwaukee on Thursday night at 7:05 CT. The game will be broadcast on WGN Radio and WCIU.
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.