Chip Kelly isn't talking about Colin Kaepernick. But rival NFL defensive coaches are after hearing of the quarterback's pairing with the new 49ers coach.

A trio of defensive coaches expressed their concern over what they feel could be a highly positive effect Kelly's read-option offense would have on the embattled quarterback's career, according to NFL.com.

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"I think (Kaepernick) is a good enough passer, but obviously what'll be a nightmare is his ability to run," one defensive coordinator said. "That offense is straight 'Freddy Krueger' when you have a quarterback that can pull the ball and run at any given time."

The quarterback-keep threat was a key ingredient missing in the Philadelphia's attack with Sam Bradford last season.

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"The fact that Kap can make guys miss and get in the open field, they didn't have that last year at all in Philly," another defensive coordinator said. "We treated [Sam] Bradford like he was under center. There was zero threat of him running the ball. We told our guys, 'Don't treat him like he's in the shotgun, he's never gonna pull the ball.' "

Kelly, himself, refused to provide any details about having Kaepernick run his system next season, leading to speculation that Kaepernick may not be around to run it. The quarterback's contract allows for the 49ers to release him before April 1 and be free of any further financial obligation.

"I'm not allowed to comment about [Kaepernick] in terms of how he fits into any system because of the CBA rules of we're not allowed to discuss football, I'm not allowed to say who fits where and how they fit," Kelly said, according to Pro Football Talk. "So I'm gonna wait until April 4 to discuss Kap and the offense."

Kelly, however, did say he was a fan of 49ers running back Carlos Hyde, according to a tweet posted to CBS Sports.

The defensive coordinators tend to agree, based on Kaepernick's ability to run.

"Now that Kaepernick is poised for a return to the zone read attack, one rival defensive coach told NFL Media reporter Albert Breer the combination with power back Carlos Hyde "could be scary."

Whether Kaepernick can be scary again remains to be seen.

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