O'Neil has spent 2013 coaching the Bills' linebackers under Mike Pettine, who was Buffalo's defensive coordinator before being announced as the new head coach of the Browns last week. It was widely speculated after Pettine's hiring that O'Neil could follow him over to Cleveland to serve as his defensive coordinator. Since O'Neil is still under contract with the Bills, the Browns had to wait for them to approve an interview.
O'Neil has spent the last five seasons with Pettine. He served as an assistant for four years while Pettine was running the New York Jets defense, then followed him to Buffalo in 2013.
Rapoport reported on Saturday that Baltimore Ravens linebackers coach Don Martindale would be the next in line for the Browns defensive coordinator position if Buffalo did not grant the interview with O'Neil.