Jack is battling a knee injury and missed Week 13 as a result.
Despite dealing with injury concerns prior to the 2016 NFL Draft that scared a number of teams away, the speedy linebacker hadn't missed a game prior to his current ailment.
Losing Jack is a significant blow to the Jaguars' defense. He leads the team with 66 tackles, adding half a sack and one interception across 11 games.
The 24-year-old signed a four-year, $57-million contract extension with $33 million guaranteed in August.