As the buzz builds that Tim Tebow could rise on NFL draft boards and be selected in the first round, Hall of Fame QB Dan Marino offered words of caution on Thursday.

Tebow won the Heisman Trophy in 2007 but his skills as a pro are in question. He's in the middle of changing his throwing motion, and analysts are split on whether he can be a good pro.

Marino told NFL.com it could be a difficult transition:

"No one is perfect. I wasn't always perfect. You get sloppy sometimes. It still comes down to making throws. Can he make those throws in tough situations?

"Yeah, you can be taught to a certain extent. The problem with that, I always tell people, as a quarterback your whole life you've been doing it a certain way.

"Now, you're 22 or 23 years old, and it's hard to change. It's really hard to change. Sometimes, under duress, you go back to your old habits."