muchas gracias ^^

I think Michelle is right, because "campo de futbol" is the field where " juegan los futbolistas" (the football players play), and the "estadio" is the "campo" and the building whole.

In fact, there is no difference in the informal language. But 'campo de fútbol' is where there is lawn. 'Estadio de fútbol' is the general environment. The total area.