Nelly Lines Up Usher, Fergie And Akon For Brass Knuckles -- But No Bruce Springsteen

'I was really trying to get the Boss, but the Boss is all over the world,' Nelly says.

Nelly and girlfriend Ashanti might make sweet music together as a couple, but when it comes down to literally making music, the two artists have only ever collaborated on one track, "Switch," a song slated for Ashanti's upcoming album, The Declaration.

Nelly says he's unsure if the two will work together again on his Brass Knuckles, due June 24.

"It's about finding the perfect song," he told MTV News over the weekend at the Kids' Choice Awards. "It has to make sense. We don't want to do it just to do it.

"You wanna make sure you get the song and you're not just agreeing because you did it [together as a couple]," he added. "It's kind of hard, because you two have a special relationship and sometimes when you work with people that you're not [as] close to, your ears are open a lot more. It is a little bit [harder], but it's also easier."

Apparently, working with Fergie and producer Polow Da Don was much easier. The St. Louis rapper described their recent collaboration, "Party People"; the video for the track premieres in two weeks.

"Energy," he said. "When I talk about energy, you got Nelly and Fergie, you probably got two of the most energetic people on the planet. And it's a straight rush."

Usher, Ciara, Akon, Jermaine Dupri, the St. Lunatics and Avery Storm are also set to appear on Knuckles. The rapper also recently revealed his ill-fated plans to work with Bruce Springsteen.

"I was really trying to get the Boss, but the Boss is all over the world," he told The Associated Press. "It didn't really work out. I know he's interested in doing it, and I'm interested in doing it."