Jadeveon Clowney has yet to sign his first NFL contract, but the former South Carolina defensive end has already impressed his coaches.

Houston Texans linebackers coach Mike Vrabel had a chance to meet Clowney before the draft earlier this month. So there were no surprises when Clowney began rookie training camp with the Texans this month. Clowney entered the franchise, walked onto the practice field and worked hard, just as Vrabel expected.

So far, Vrabel said, he's impressed with Clowney's attitude as much as the physical gifts.

"I think his attitude, much like all of our guys, their attitude has been great," Vrabel told ESPN.com on Thursday. "They've come in, they've tried to be vocal in the meeting rooms, not always right, but at least they have the confidence to try to make the calls, make the adjustments and make the corrections while we're in there. He's somebody that we're excited about because he has the natural ability, but he also has the attitude to want to learn. He doesn't think he has it all figured out."

Vrabel is the perfect position coach for Clowney, who's making a transition from defensive end to outside linebacker in Houston's 3-4 defense. It's the same transition Vrabel had to make when he entered the league from Ohio State in the late 1990s. He was successful, helping lead the New England Patriots to three Super Bowls in a four-season span.

Vrabel was asked about the knocks on Clowney's work ethic. He didn't answer them specifically, but said he isn't concerned with any issues regarding Clowney's work ethic. With the Texans, he said, Clowney won't have a choice but to go full throttle every snap.

"Effort is something that we're not going to sit here and coach," Vrabel said. "We're not going to coach effort on our defense. I think anybody, the 11 guys that we put out on our defense, [defensive coordinator] Romeo Crennel and our head coach, we're going to make sure they're playing with great effort."