According to Clayton, Allen was at odds with team management about his assistants and the length of their contracts.
Allen, whose contract ends in 2015, wanted the assistants to receive two-year contracts. Instead, a number of assistants chose one-year deals, according to the report.
Allen, 41, has led the team to identical 4-12 records in his two seasons with the Raiders. The team has not made the playoffs since 2002. That year they lost in the Super Bowl to the Tampa Bay Buccaneers.PHOTOS: Fired NFL Head Coaches