"I was kind of struggling up here for a while," Miller said. "I'm surprised I obviously stayed up here this long."
The D-backs entered the year counting on Miller to provide a boost to the starting rotation in an attempt to become a winning team. That's why they traded a hefty package -- one including last year's No. 1 overall pick Dansby Swanson -- to Atlanta in the offseason to acquire the 25-year-old.
Instead, Miller went 2-9 with a 7.14 ERA -- the highest of any pitcher in the National League with at least 14 starts. He posted just two quality starts in those 14 outings, spent some time on the disabled list in June with a sprained right index finger and never looked like the top-notch starter he was in St. Louis and Atlanta over the past three years.
"We just have to find a way to getting him back to pitching the way he can," Arizona manager Chip Hale said before his team's workout at Chase Field on Thursday. "It's a disappointing move for us to make as coaches. You always feel like we're here to make them better ballplayers and pitchers, and we've dropped the ball with him. Obviously it's something that hurts. It's not easy for a guy that's had that much success in the big leagues."
Miller entered the season with a 3.22 career ERA. Although he was 6-17 with the Braves in 2014, he had a career-best 3.02 ERA and made his first All-Star appearance.
Miller wants to get back to having that type of success. In order to do so, he'll have to earn back a spot in the D-backs' rotation by pitching well in Reno -- which Miller hopes won't take long. Hale said there's no timetable for it.
"For me, personally, to go down there, obviously you never want that to happen," Miller said. "My goal is to go down there, figure some things out, and get back here as quick as possible."
The D-backs will go with a four-man rotation (Patrick Corbin, Archie Bradley, Robbie Ray, and Zack Godley), with off-days approaching on Monday and next Thursday, until they need a fifth starter.
Left-hander Edwin Escobar will be recalled from Triple-A on Friday to take Miller's spot on the D-backs' roster. He will be working out of the bullpen, Hale said.
• Outfielders David Peralta (lower back strain) and Chris Owings (plantar fasciitis) both played in the Arizona Rookie League on Wednesday and Thursday. Hale said they will both have a rest day on Friday before beginning rehab assignments at Triple-A Reno on Saturday.
• Starter Rubby De La Rosa (right elbow inflammation) has been throwing from 120 feet. He said he expects to throw his first bullpen session next week.