"She is deeply concerned about the direction the show has been taking," a source toldPeople of the professional trainer. "She is turned off by the mean-spirited story lines and poor care of the contestants."
The claims follow The Biggest Loser's controversial fifteenth season in which Rachel Frederickson, 24, won the show but dropped down to a shocking 105 pounds to do so. Frederickson had lost nearly 60 percent of her body weight for the finale two months ago, concerning both her trainers and viewers.
According to E! News, the incident led producers to begin considering some "small but significant tweaks" to the show.
But still, "Michaels wants to distance herself from The Biggest Loser brand," explained the source. "Especially considering what happened with Rachel, her feeling is that there isn't proper attention paid to the contestants' health or wellness."
In 2006, Michaels, 40, left the series after Season 2 due to a dispute about the show's creative direction. While she was replaced by trainer Kim Lyons for the show's third edition, she subsequently returned for Season 4 and stuck with it right up through Season 11.
However, Michaels left again after the show's eleventh edition for personal reasons that included starting a family. She returned to The Biggest Loser for Season 14 last year.
"They asked her to come back to boost the ratings and they needed her, but the Rachel thing shook her up," the source told People.
Michaels expressed her anger regarding Frederickson's drastic weight-loss to The Tennessean newspaper in late February.
"I was furious on a bunch of different levels because I felt like, how did we not know? How did the show fail her? It's obvious we believe she's too thin. It's absurd on many levels, for her and how this happened, and I'm concerned about why we weren't told," Michaels said at the time.
Michaels also reportedly doesn't like how The Biggest Loser has portrayed her as a trainer -- tough as nails and all business.
"The show uses her as the bad guy, and anyone who knows Jillian knows she's not the bad guy at all," the source told People. "She's a loving mother of two kids. She's not the negative person they portray her as. She wants to be in a place where she has more respect."
NBC representatives in addition to Michaels reportedly declined comment on the status of the trainer's continued The Biggest Loser participation. The show's sixteenth season is currently casting and expected to air this fall.