D-Backs demote struggling Miller to Triple-A

Shelby Miller's lousy season took another turn for the worse Thursday, as the Arizona Diamondbacks optioned the struggling right-hander to Triple-A Reno roughly 24 hours before their second half was set to begin.

Miller, an All-Star in 2015, has been a major disappointment this season for the Diamondbacks, who dealt two top prospects - including last year's No. 1 pick Dansby Swanson - and outfielder Ender Inciarte to the Braves in exchange for the 25-year-old starter.

In 14 starts this year, Miller's allowed 55 runs over 69 1/3 frames while averaging more than four walks per nine innings. Among pitchers with at least 60 innings, Miller's 7.14 ERA is the third-worst in baseball.

"I'll take the time to go down there and work things out and hopefully come back pitching better obviously," Miller told MLB.com's Jake Rill on Thursday. "I was kind of struggling up here for a while. I'm surprised I obviously stayed up here this long."

Miller's disastrous season has been a microcosm of the Diamondbacks' disappointment as a whole. Outside of Zack Greinke, who rediscovered his form prior to landing on the disabled list earlier this month, the club's rotation has been a mess, compiling the third-worst ERA (4.94) in the National League and fifth-fewest WAR (4.4).

Considered by many as a legitimate preseason threat to win the West, the Diamondbacks hit the break in last place, 19 games behind the division-leading Giants.

''I told him we're not going to be the team that we envisioned without him being who Shelby Miller can be,'' manager Chip Hale said. ''That was my message.''

In a corresponding roster move, the club promoted left-hander Edwin Escobar to replace Miller in the rotation.