While a newly fit and fabulous Britney Spears appears to be staging a career comeback, her soon to be ex-husband, Kevin Federline, is hanging on by a very thin thread.

He might not get to continue that Gucci-wearing, high-rolling lifestyle he brags about in his rap songs. And his career — cue the eye rolls — is not taking off as he'd hoped.

After two years of marriage, Federline, 28, went from K-Fed to Fed-Ex on Tuesday when Spears filed for divorce in Los Angeles, citing "irreconcilable differences." The 24-year-old pop princess is seeking custody of their two young sons, with visitation rights for Federline.

That's bad news for Fed, a backup dancer-turned-rapper who's been tagged as a party-loving bad boy and well-kept husband. There appears to be a prenuptial agreement, which "probably contains a waiver of alimony, but we don't know that," said Bethesda, Md.-based divorce lawyer Glenn Cooper. "If he waived it, he won't get it."

Federline's debut album, released on Halloween, sold a dismal 6,500 copies its first week, according to Nielsen Soundscan.

He can't blame lack of publicity for the poor sales. "I think there are very few people who don't know that he has a record out," said Leah Greenblatt, a music writer at Entertainment Weekly magazine.

"I don't think he needs to publicize the fact that an album exists by Kevin Federline," she said. "But I haven't heard of any sort of appearance that he's made where he hasn't been heckled and booed ... he just strikes me as either completely clueless or just incredibly tenacious. And possibly deluded."

The guy also is having a tough time finding a friendly audience. Amid a chorus of boos, he was body-slammed last month by wrestler John Cena in an appearance on "WWE Monday Night Raw." He had to cancel a concert this week at a House of Blues in Cleveland, Greenblatt said, because of low ticket sales. He played to a nearly empty house at New York City's Webster Hall last weekend. And at his album release party at a New York club last Friday — no sign of Brit, by the way — the crowd was more excited about dancing to popular hits than listening to Fed's rhymes.

Gary Bongiovanni, editor of Pollstar, which tracks concert tour schedules and sales, called him a "curiosity factor."

A Federline music future is not in the cards, Bongiovanni said, "unless there is a demand out there or somebody who believes in him and is willing to take a chance and willing to buy a whole tour of K-Fed and take him around the country."

"In fact," he added, "I'd almost expect him to drift away into obscurity. He gets a hit record, that changes everything. Absent that, you know, he gets divorced, there goes the curiosity factor."

What should Federline do next to remain in the spotlight?

In September, he guest starred on "CSI: Crime Scene Investigation," so he might try acting. Or he could return to his former profession: backup dancer to tried-and-true stars such as Christina Aguilera. "That's one genuine talent that he did have," Greenblatt said.

Semi-pro wrestler? Nah. Handbag designer? That's a low blow. Reality TV star?

That's more like it, says Greenblatt. "I don't see him as being that far below someone like Omarosa (from "The Apprentice") on the Hollywood food chain once the fallout settles."