NICOLE RICHIE was hoping for a major career boost when she signed on as a mentor and judge on NBC’s “Fashion Star,” but she may not return for the reality show’s second season because she can’t stand camera hog JESSICA SIMPSON!

“Nicole doesn’t see how there’s room for both of them on the set,” a source told The ENQUIRER. “Nicole is relatively de­mure and collected, while Jessica is so over the top she just sucks the air out of the room.

“As the show progressed, Nicole saw herself be­coming second banana to Jessica, and that’s not what she signed on for.”

Nicole, 30, and Jessica, 31, taped “Fashion Star” last summer, and as Nicole watched the season play out on TV, she found her­self disappointed.

“It was pretty obvious to Ni­cole that the producers had the show ed­ited to make Jessica the focus,” the source said.

And Nicole fears things will be even worse next season when Jessica starts “blabbing” about her new daughter,  Maxwell, who was born on May 1.

The two women have had parallel careers in that both were reality stars who went on to launch their own fash­ion lines. But while Jessica’s empire is worth an estimated $1 billion, Nicole’s House of Harlow only brings in about $2 million annually.

“Nicole originally believed that by doing the show, she could increase the visibility of her line and maybe score some product endorsements or acting jobs,” the source maintained. “But she hasn’t gotten the boost she wanted.”

The two women haven’t clicked behind the scenes either, says the source.

Jessica “pretty much ig­nored Nicole,” while Nicole – mom to 4-year-old daugh­ter Harlow and 2-year-old son Sparrow – was less than thrilled over how much at­tention Jessica was getting just for being pregnant.

“Nicole says Jessica acts like she’s the first woman to ever have a baby,” added the source. “She’d rather jump ship now than watch Jessica be Queen Bee next season.”