I think the problem is that they eat, and/or they work out...so they have some abs. What is your idea of no-gut? Stretched out like Alexander Popp, Lars Burgsmuller or Ivo Karlovic?
On a superficial note, I find most of the tennis players absolutely gorgeous! Male and female, they've got nothing to be ashamed of, they look great (especially when 40-60% of australians are obese *allegedly* and with supersized americans... these players are role models).The few that might actually have a slight gut, would be the older ones... Landsberg for example