Gilbert, who was the No. 8 pick in May's NFL draft, played just 17 snaps against the Carolina Panthers last Sunday, a decision that Mike Pettine said was partly made based on the rookie's preparation.
"It's time to grow up and not be a kid anymore. It's a wasted year for him," Whitner said. "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 [Dansby] 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."
On Monday, Dansby told reporters that he doesn't know if Gilbert can make the transition from college to the NFL, and that the rookie has to have the will to make the change himself.
The Browns are leading the NFL in interceptions with 21, only one of which belongs to Gilbert. The cornerback also has 29 tackles this season.
Cleveland is 7-8 heading into its season finale against the Baltimore Ravens on Sunday.
- Molly Geary