Kevin Federline and Britney Spears

Britney Spears shops at a toy store in Malibu.

Kevin Federline has revealed that his marriage to pop princess Britney Spears' needs work'.

Over the past year there have been multiple reports that the couple's relationship is in trouble, and Federline has admitted that they find it difficult to spend time together due to their hectic schedules.

The aspiring rapper's second child with 24-year-old Spears is due next month, and he worries this will test them even further.

"It's definitely going to be hard. It'll have to be worked at, but that's every relationship," Contactmusic quotes him as saying.