Cox leads the Jaguars in interceptions with two while Mathis is the all-time franchise leader with 30 career interceptions.
The Jaguars ruled out the possibility of cornerback Rashean Mathis playing against the Detroit Lions on Sunday and listed cornerback Derek Cox will be listed as questionable for the game, according to Ryan O'Halloran of the Florida Times-Union.
In the event that neither player is available to start, the likely pair of starting cornerbacks would be William Middleton and Aaron Ross. Middleton earned the start for Week 8 when Derek Cox was unable to play against the Packers.
After both players were limited in practice on Wednesday, neither Mathis nor Cox practiced with the team on Thursday. Mathis left Sunday's game against the Packers with a groin injury, while Cox was out with a back injury that was suffered in Week 7 against the Raiders.
On Sunday, the Jaguars will likely The 2012 Jaguars defense ranks as the No. 23 unit against the pass, although they are No. 10 in passing touchdowns allowed, having given up only nine.