When manager John Gibbons was asked about the decision, he said Delabar's name had been discussed as a possible callup, but the club ultimately wanted him to rest and regroup for 2015.
"You can't bring everybody," Gibbons said. "With Delabar, the whole idea is let him go home and rest. It was kind of a tough year for him up here and down there it was kind of mixed results. We figured he might be better off, going home and resting, getting ready for next year."
Delabar began the season in the big leagues, but he never settled into the type of groove that made him one of the game's elite setup men in 2013. Delabar struggled with his control at times and posted a 4.91 ERA in 25 2/3 innings before getting buried in the Minors.
The native of Kentucky remains under club control next season and will presumably compete for a spot in the bullpen.
"I think the big thing was just the strike throwing and it had gotten better overall," general manager Alex Anthopoulos said. "You look at the numbers, he's got an ERA below three and I watched his last outing on Monday and it looked better, the split looked like it was back.
"There was some discussion with respect to maybe he just would be best suited to just take a break. He's thrown a lot if you look at how much he threw last year. Clearly, he's had another full season again."
Gregor Chisholm is a reporter for MLB.com. Read his blog, North of the Border, and follow him on Twitter @gregorMLB. This story was not subject to the approval of Major League Baseball or its clubs.