If it looks like a 'Duck car' then it must be Jonathan Stewart's new ride

Stewart shows off his Oregon Duck-themed car (0:18)

Panthers running back Jonathan Stewart rolled into training camp with a yellow and green car paying homage to Oregon, where he played football. (0:18)

SPARTANBURG, S.C. -- The "Duck test" for centuries has been used as an amusing form of logical reasoning. You know: "If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck."

The same test can be used for Jonathan Stewart's new car.

You know: "If it looks like a Duck car, drives like a Duck car, and quacks like a Duck car, then it probably is a Duck car."

OK, the horn doesn't quack.

But make no mistake, the Carolina Panthers running back said, when he shows up in the green, gray and yellow Audi it screams one thing.

"Ducks," Stewart said with a smile.

The 30-year-old Stewart turned a lot of heads when he arrived at training camp in what he called his "Duck Mobile" that takes a page from the outlandish Oregon Ducks jerseys made by Nike.

A 2008 first-round pick out of Oregon, Stewart loves his Ducks and the car is just an extension of that. A longtime customer of Audi, the manufacturer helped him out with the one-of-a-kind features that were designed by a friend.

Carolina coach Ron Rivera, who attended Cal, isn't so sure about the car.

"I'm a little concerned about that," he said. "If I was the manufacturer of the car I'd be concerned. I'm saying that as a Pac-12 [rival]."

Stewart loves the car that features duck wings on the rearview mirror and the word Ducks on the door handle with a splash of yellow.

His favorite feature?

"Those wings on the mirror," Stewart said.

It definitely looks like a Duck car.

Maybe one day Stewart will add a quacking horn and it'll even sound like a Duck car.