JACKSONVILLE, Fla. -- Jacksonville Jaguars coach Doug Marrone still isn't completely sure what the team is going to do at middle linebacker in 2018.

Myles Jack manned that spot last season whenever the Jaguars had five defensive backs on the field but lined up at strongside linebacker in the team's 4-3 base defense. It turned out pretty well: Jack was the Jaguars' second-leading tackler in both the regular and postseason.

The Jaguars could use that formula again, or they could move Jack to the middle permanently. The most important thing, Marrone said, is that Jack's development in 2017 has the team confident that he can handle any role they give him in 2018.

"I thought, in my mind, that Myles took a really good step in the right direction and stepped up last year," Marrone said. "I thought he played really well for us. And I think that if we left Myles at SAM at regular personnel and put him at MIKE in nickel, that's fine. If we moved him in there for all three downs now, if we have someone that we feel we can put at SAM, whether it's Blair [Brown] or whether it's someone that's not here yet, we have the ability to do that."

The Jaguars originally planned on Jack taking over as the full-time middle linebacker last season, which is why they moved him inside and moved Paul Posluszny -- who had never played outside linebacker in his 10-year NFL career -- to strongside linebacker during organized team activities last spring. Jack played only 230 snaps as a rookie on defense in 2016 at strongside linebacker but the Jaguars wanted to take advantage of his speed, athleticism and coverage ability by moving him inside.

It wasn't an easy transition, especially in terms of making pre-snap adjustments and checks and communicating those changes to the defense quickly. Jack gradually improved throughout training camp and though he missed several tackles and took a few bad angles to get to ball carriers, Marrone and Posluszny both said Jack played at a high level in the preseason opener against New England.

Yet two days after that game the Jaguars moved Posluszny back to middle linebacker and Jack back to strongside linebacker in base defense as defensive coordinator Todd Wash tinkered with the lineup to get the best combination on the field. That plan stuck throughout the 2017 season and Jack finished with 90 tackles, three pass breakups, a fumble recovery, and two sacks.

Jack had a sack, an interception, and a forced fumble in three playoff games. He made what could have been the game-turning play against New England in the AFC Championship Game when he ripped the ball out of Patriots running back Dion Lewis' hands, but the offense went three-and-out following the turnover.

Marrone said where Jack lines up in 2018 depends on the development of second-year linebacker Blair Brown and whether the team drafts a linebacker or adds one later. Marrone said the lineup today would be Jack at middle and Brown, who played mostly special teams in 2017, would be the strongside linebacker.

He has no doubt that the experience Jack gained in 2017 will make Jack's transition to a full-time middle linebacker much easier this year than it was last season.

"That's something that we feel comfortable with," Marrone said. "We're going to play the best three [linebackers]. We have good versatility again."