According to Jaguars.com it is "not an injury related" situation but instead "a violation of team rules" that will keep Fournette from playing Sunday. Doug Marrone was typically curt about the situation.
According to Field Yates of ESPN, one of the reasons the Jaguars deactivated Fournette is because the running back missed the team photo. Which is something they were taking on their bye week in November, apparently.
Amongst the reasons Jaguars RB Leonard Fournette is out today is that he missed the team photo earlier this week, sources confirmed to ESPN.— Field Yates (@FieldYates) November 5, 2017
Fournette has been battling an ankle injury but recently told the CBSSports.com Pick Six Podcast (subscribe on iTunes here) that he was planning on playing against the Bengals after the Jaguars Week 8 bye. The expectation was that the Jaguars offense would lean heavily on Fournette against Cincy. Instead, it is Chris Ivory who is going to get the start for Jacksonville.
There are some concerns among members of the organization, according to Ryan O'Halloran of the Florida Times-Union, that things could "unravel" for Jacksonville. (O'Halloran later deleted the tweet.)
It's not inconceivable: Fournette is the sixth-leading rusher in the NFL and is averaging 4.6 yards per carry. He's the guy who makes the Jaguars offense go and losing him is going to cause issues for the offense. Ivory is a nice player and expect to see T.J. Yeldon contribute here as well, but this puts a lot of pressure on quarterback Blake Bortles and puts even more pressure on the defense to limit what Andy Dalton and the Bengals do.
Jags' RB snaps/touches Week 7 without Fournette:— Graham Barfield (@GrahamBarfield) November 5, 2017
Ivory - 57% snaps; 17 touches
Yeldon - 34% snaps; 11 touches
Grant - 12% snaps; 7 touches
Worth noting on the Vegas side of things is that the Bengals are now +4.5 in this game, whereas they were +5.5 points earlier in the week.