Hermanson agreed to a Minor League deal with the Reds on March 1, with an invitation to camp so he could compete for the closer's job. He started well, but struggled in his last few appearances.
The 34-year-old pitcher ended Spring Training with a 7.36 ERA. The Reds wanted him to open the season with Triple-A Louisville, but Hermanson wanted to be released instead.
"We hoped that if he didn't make our club he'd go to Louisville and pitch for us, but he just had no interest in it," manager Jerry Narron said. "We were all hoping that he had the same form he had a couple of years ago, but as Spring Training wound down to the end, we just didn't see it."
Hermanson was the Chicago White Sox closer in 2005, when they won the World Series. He developed back problems that wiped out almost all of his 2006 season and made teams wary of signing him.
Hermanson invited teams to watch him throw at his home in Arizona during the offseason. None was interested in offering a Major League deal, but the Reds were willing to give him a chance and invited him to camp.
They told him of their decision early Sunday morning.
"It was tough to tell Dustin Hermanson he was not going to make the team," general manager Wayne Krivsky said. "We wanted him to step up. Unfortunately the last two or three times [he pitched], we had concerns.
"That was a very difficult thing to do. We were all pulling for him. It would have been another nice story."
The Reds needed a closer because left-hander Eddie Guardado is recovering from reconstructive left elbow surgery and won't be ready to pitch for at least a couple of months. Left-hander Mike Stanton and right-hander David Weathers also can close games.