"It's not any ligament damage, but it's still enough to be out for some time," head coach Marrone told reporters Monday. "That's about all I'll give out. I might give you more later when I get more specific [details]."
The 23-year-old already dealt with a knee injury this season that cost him two games, though he has otherwise been fairly durable in his career.
After Jacksonville selected Allen with the No. 7 overall pick of the 2019 draft, he appeared in all 16 games as a rookie and earned a Pro Bowl nod as an important building block for the team's future.
The Kentucky product tallied 44 tackles, 10.5 sacks and two forced fumbles in his first year in the league but has followed with just 2.5 sacks and 11 quarterback hits in eight games this year for a Jaguars team that has disappointed and appears to still be in the early stages of a rebuild.
If Allen is sidelined with this latest setback, look for the combination of K'Lavon Chaisson, Adam Gotsis and Dawuane Smoot to see more playing time along the defensive front.