Gronkowski reportedly suffered a ruptured disk against the Seattle Seahawks on Nov. 13, according to Vic Carucci of the Buffalo News.
Gronkowskireaggravated the injury in Week 13 against the New York Jets. He played seven snaps and received two targets before leaving the game.
The team initially believed the injury was not as serious and he would return quickly but Gronkowski is now expected to miss eight weeks. There is no timeframe for his return, according to ESPN's Adam Schefter.
Gronkowski missed Week 11 against the San Francisco 49ers due to a chest injury.
He has 25 catches for 540 yards and three touchdowns on the season.