The team later confirmed the move on its Twitter page.
"Kamerion is a great young talent, and (we) are excited about him continuing his career as a member of the Silver and Black," coach Hue Jackson said.
The Raiders initially had exercised a $3.5 million buy-back option on Wimbley, which was intended to keep him off the free-agent market.
The NFL Management Council ruled that the buy-back violated the 30-percent rule and voided it, which meant Wimbley, a fifth-year pro who led the Raiders with nine sacks in 2010, likely would have been eligible for unrestricted free agency under a new collective bargaining agreement.
To prevent that, the Raiders opted to franchise him. Wimbley intends to sign the tender -- it will be worth approximately $10 million -- shortly, according to a source. The sides are continuing to discuss a long-term deal to keep him in Oakland.