The Oakland Raiders have the only head coaching vacancy left in the NFL.

With Denver's hiring of John Fox on Thursday, six of the seven head coaching vacancies have been filled this offseason. Earlier Thursday, the Cleveland Browns hired Pat Shurmur as coach.

The Raiders announced last week they were not picking up a $5 million, two-year option to retain coach Tom Cable. Cable went 17-27 in two-plus seasons. He led the Raiders to an 8-8 mark in 2010, Oakland's best record since 2002.

"The interview process is ongoing," senior executive John Herrera said. "We have been doing our due diligence with our current assistant coaches. That process has been ongoing all week."

Offensive coordinator Hue Jackson is considered a favorite to get the head coaching job. He is under contract as an assistant already for next season.

The contracts of many of the other assistants, including defensive coordinator John Marshall, expire next Tuesday. Marshall could be in jeopardy after the Raiders allowed at least 30 points in six of their eight losses.

Jackson came over after last season and assumed the play-calling duties from Cable. The improvement on offense was the biggest reason why the Raiders won three more games than they had in any of the previous seven seasons.

Led by quarterback Jason Campbell, a breakout season from running back Darren McFadden and big plays from rookie receiver Jacoby Ford, the Raiders finished sixth in the league in scoring with 410 points. That was the sixth-most points scored in a season in franchise history and more than doubled the 2009 scoring output.

If Jackson does get the job he would be the sixth first-time NFL coach out of the seven hired this offseason, with Fox being the only experienced candidate.

The Vikings and Cowboys kept their interim coaches with Leslie Frazier staying on in Minnesota after replacing Brad Childress during the year and Jason Garrett keeping the Dallas job he took over from Wade Phillips.

Two teams went the NFL coordinator route, with Shurmur replacing Eric Mangini in Cleveland and Ron Rivera taking Fox's place in Carolina. San Francisco went to the college ranks to hire Jim Harbaugh from Stanford to replace Mike Singletary.

The other big development for the Raiders so far this offseason was the news that the final year of Pro Bowl cornerback Nnamdi Asomugha's contract had voided because he did not meet certain incentives.

The Raiders previously had an option for 2011, which would be worth either $16.8 million or the amount of the quarterback franchise tag, whichever is greater.

Now Asomugha will be an unrestricted free agent. The Raiders can either sign him or likely receive a compensatory draft pick in 2012 if he signs with another team.

Asomugha was paid $28.5 million in the first two years of the contract.