"It's time to grow up and not be a kid anymore. It's a wasted year for him," Whitner told ESPN.com. "There were so many ups, so many downs -- a lot of it has been brought on by himself.
"He has to look himself in the mirror like Karlos said, he has to understand what he did wrong, what he needs to get better at, and make sure that you're back here working out from day one when we return here to show everybody you have a good attitude and you want to go out there and be the player they drafted you to be."
Gilbert played just 17 snaps against the Panthers. Browns coach Mike Pettine said Gilbert didn't break a team rule last week but said both on- and off-the-field issues have played a part in his diminished role. Gilbert failed to beat out Buster Skrine for a starting spot opposite Joe Haden during training camp. Undrafted rookie K'Waun Williams won the nickel job, locking Gilbert into a reserve role.
Whitner was asked if Gilbert's rocky rookie campaign went beyond typical rookie growing pains.
"Yeah, but you know we keep all that in house," Whitner said.