Pop star Jessica Simpson is set to join her boyfriend Tony Romo on the American football field - she has signed to star alongside him in a new sports show.

Simpson was criticised for supporting the Dallas Cowboys quarterback from the stands last year, when her attendance coincided with a losing streak.

But the negative press hasn't put her off agreeing to appear in an episode of U.S. TV show Hard Knocks - a series that shows fans the inner-workings of American football camps.

And HBO network boss Ross Greenburg insists the focus of the program will remain the same, despite its celebrity line-up.

He says, "I'm telling you, we are going to attack this Hard Knocks the same way we have attacked all of the other Hard Knocks. We're not going to make this an E! half-hour entertainment show on Tony Romo and Jessica Simpson."

Simpson's episode is set to air in the U.S. on Wednesday.