"He was one of the better starting pitching prospects in all of baseball as recently as a couple of years ago," Epstein said. "We feel like that talent's still in there. If you look at his velocity, it's still there. If you look at some of his peripheral numbers, they're still pretty decent."
Turner was 4-7 with a 5.97 ERA in 20 games (12 starts) with Miami this season, striking out 54 over 78 1/3 innings.
"He's just 23 years old," Epstein said. "He's got a really good arm, and we feel like we got him at a low point of value and there's plenty of upside left with him. We're excited about that."
Picked ninth overall by the Tigers in the 2009 First-Year Player Draft, Turner was pushed through the Minor Leagues quickly, making his Major League debut in 2011 at the age of 20. Turner was dealt to Miami in July 2012 as part of the Anibal Sanchez-Omar Infante trade.
This season, Turner was 4-5 with a 6.03 ERA in 12 starts, and he had a 5.74 ERA in relief.
"He's had an accelerated development path because of the Major League contract he signed coming out of high school," Epstein said. "We've had some success with talented pitchers who are going through tough periods, just getting them here, letting them reset a little bit [and giving] them some different things to think about, whether it's a different grip or a different spot on the rubber -- just boosting their confidence and letting them be themselves and go pitch."
Pitching coach Chris Bosio and his staff will try to help Turner get on track, as they did with Jake Arrieta, Jason Hammel and Scott Feldman. Chicago acquired Arrieta from the Orioles in a similar trade a year ago, and he's now fronting the rotation following the trade that sent Jeff Samardzija and Hammel to Oakland last month.
"We're hopeful that will happen with Jacob," Epstein said. "It might not happen right away, but certainly I think between now and next Spring Training, there are some things we can work together on to get him back to a place where he can have success."
Justin Ruggiano, one of Turner's teammates in Miami, knows the right-hander well.
"He was a teammate of mine, and a great teammate, and he's a competitor out there on the mound," Ruggiano said. "He's so young, and he was a big piece in that Anibal Sanchez trade. That may have come with a little bit of pressure and may have caused him to press; I don't know.
"I'm sure he's capable of pitching at a high level," Ruggiano said. "Sometimes it takes guys a little longer to figure it out. I played against Cliff Lee when he was in Triple-A, and all of a sudden, he's making $140 million twice. This game is crazy. I think Jacob has the personality that, given another opportunity, he'll do OK with it."