The Forest striker suffered an ankle injury in his side's Championship clash with Wolves and will be sidelined for eight weeks as he recovers
The 25-year-old attacker departed on a stretcher after colliding with Wolves defender Kevin Foley and was taken for scans in order to discern the extent of the injury.
Cox tweeted on Wednesday to announce that he would miss the next two months as he begins his recovery.
"I am out for around two months," the Republic of Ireland international revealed on Twitter. "But [the injury] feels better and better each day."
Cox joined Forest from Premier League side West Brom at the beginning of the 2012 season and has gone on to score five goals in 17 games for his new club.