On Thursday, ESPN's Adam Schefter reported the league is "now looking into" the process Oakland used to hire Gruden and whether it violated the Rooney Rule.
The 53-year-old originally joined Oakland in 2007, serving as the team's offensive line coach in 2007 and the first portion of 2008 before taking over as head coach during the latter season after Lane Kiffin was sacked.
Cable has spent the last seven seasons working as the assistant head coach/offensive line coach for the Seattle Seahawks before being dismissed on Wednesday.
It was a special day, as hordes of media members, and north of 50 Raiders alumni filled up the team's performance, center anxious to see the newest leader of the coaching staff.
Gruden succeeded Jack Del Rio, who was sacked following a season-ending loss to the Los Angeles Chargers that capped a disappointing 6-10 campaign for the Raiders.
Cable returning to the Raiders seemed highly unlikely after late owner Al Davis detailed Cable's misgivings in a post-firing press conference.
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Cable's tenure included allegations of physical abuse. Cable was allegedly involved in a 2009 incident where then Raiders assistant Randy Hanson was left with a broken jaw. Cable finished out his final season.
Gruden was introduced last Tuesday as the franchise's head coach.
That will mean a reunion between the Seahawks and Cable for the Seattle-Oakland game in London next October 14.
The hiring of Cable will also net a happier running back in Marshawn Lynch, who had his glory years in the Pacific Northwest with Cable as his offensive line coach.
Lynch did not mesh as quickly in his first season behind the Raiders' high-paid offensive line in 2017.
The Seahawks fired Cable along with offensive coordinator Darren Bevell after finishing 9-7 to miss the playoffs for the first time since 2011.