Still, the organization sees a tremendously gifted player who is looking to put it all together.
The 6-foot-7 former first-round Draft pick is coming off a rough season. He dealt with a demotion to Triple-A New Orleans in July, and then a Minor League disabled list stint due to a right ankle injury. When he returned to the roster, he was used in a relief role.
Miller finished 3-5 with a 4.84 ERA in 20 games, with 14 of them starts.
In hopes of getting Miller on track, the Marlins have sent the lefty to the Arizona Fall League, where he will pitch for the Mesa Solar Sox.
"I've been given a lot of opportunities. I haven't necessarily taken them and run with them yet," Miller said. "But I still think I'm young. I think I have plenty of time to hopefully keep working towards that goal."
When the Marlins acquired Miller from the Tigers in 2007, they were hopeful that he would be a top-of-the-rotation starter. In the blockbuster deal for Miguel Cabrera and Dontrelle Willis, the Marlins received Miller, outfielder Cameron Maybin, pitcher Burke Badenhop and three other prospects.
Thus far, Miller's first two years with the Marlins have been a struggle. He's a combined 9-15 with a 5.43 ERA in 49 games with 34 starts.
Miller opened 2009 as the Marlins' fifth starter, and he will be given a chance to win a rotation spot in Spring Training.
The history of the game is replete with examples of pitchers who took a while to put it all together.
Randy Johnson, who broke into the big leagues with the Montreal Expos in 1988, labored a couple of seasons and was dealt to Seattle. In 1990, at age 26, Johnson had his first breakthrough season, going 14-11 (3.65) in 33 starts.
Sandy Koufax was 25 when he broke out with an 18-13 season for the Dodgers in 1961.
Not to say Miller's career will at all mirror those of Johnson or Koufax, but they, too, took a while before experiencing consistent big league success.
Like the 6-foot-10 Johnson, Miller is a rangy left-hander who has dealt with command issues early in his career.
An objective in the Fall League is to get Miller some innings while having him refine his delivery.
"I think there are some mechanical problems that are hampering me from throwing pitches where I want to," Miller said. "It's just a process. You have to figure it out as you go."
Because he was optioned to the Minor Leagues in July, and spent time on the disabled list, he was limited to 80 innings at the big league level. For the Zephyrs, he made three starts and was 1-2 with a 7.71 ERA.
And his total Minor League innings, counting some rehab appearances, was 28 2/3. So, he finished 2009 with a total of 108 2/3 innings.
Miller also had limited work in 2008, finishing with 107 1/3 innings with the Marlins, plus another 19 1/3 innings in the Minor Leagues.
The Fall League will give him a chance to build up some innings.
"I haven't thrown that much in general," Miller said. "I've got some things that I'm working on mechanically. In general, my ultimate goal is to throw more strikes.
"It hasn't been easy. I don't think I expected it to be. It is what it is. You try to make the most of it, learn from it, and eventually figure it out.