Steve Zahn: Matthew McConaughey Will Be an 'Awesome' Father

WEDNESDAY JANUARY 16, 2008 05:10 PM EST

Matthew McConaughey will be "an awesome dad," his Sahara costar Steve Zahn tells PEOPLE. But there's just one problem.

"[Babies] like to bite and grab your shirt, so he'll have to wear a shirt," Zahn jokes. "But now he'll have an excuse to take it off, because they'll throw up on it."

McConaughey, 38, announced Tuesday that girlfriend Camila Alves, 24, is three months pregnant. Zahn suggests McConaughey will have to work extra hard to maintain his famous abs.

"It's easy to work out when you're single and you've got time and money. When your kids are screaming and you're up from 2 to 5 a.m., it's a little harder to work out," the Strange Wilderness actor and father of two says. "It's great having kids, but man, those first two years are tough! It's a big transition. It's just endurance."

The toughest part? "All of the sudden nothing you do is that important anymore," says Zahn, 40. "It's all about your kids. It's just a tough adjustment at first, but it's a beautiful thing."