JACKSONVILLE, Fla. -- The Jaguars are signing Myles Jack to a contract extension that makes him the third-highest-paid inside linebacker in the NFL, a league source told ESPN's Adam Schefter.

The four-year extension through 2023 is worth $57 million and includes $33 million guaranteed. Jack will make $14.25 million annually when the extension kicks in, which trails only Bobby Wagner ($18 million) and C.J. Mosley ($17 million) in annual salary among inside linebackers.

The Jaguars announced the extension Monday but did not disclose terms.

"We're excited to have Myles in Jacksonville for the foreseeable future," Jaguars executive vice president of football operations Tom Coughlin said. "This was something that we wanted to get done because Myles has proven himself to be a key component of our defense. His versatility and durability are both traits that we value on the football field, but Myles is also committed to bettering our community and I know he's pleased with the opportunity to stay in Jacksonville and continue to make a positive impact on our city."

Jack's deal is slightly smaller than the one the Dallas Cowboys gave linebacker Jaylon Smith earlier this month. Smith signed a five-year extension worth $64 million that includes $35.5 million guaranteed. Jack and Smith were both regarded as potential first-round picks but were drafted in the second round in 2016 after concerns about knee injuries, and both were entering the final year of their rookie contracts.

Per ESPN Stats & Information research, the six largest contracts at inside linebacker have all been signed this offseason. Deion Jones, Anthony Barr and Kwon Alexander also got new deals.

Jack has never missed a game in his three seasons and has started 42 games (the past 34 in a row) in the regular season. He has 219 tackles, five sacks, two fumble recoveries and one interception. He also has 16 tackles, one sack, one interception and one fumble recovery in three playoff games.

Jack played all three linebacker spots as a rookie in 2016 but was moved to middle linebacker permanently in 2017. He already has earned his spot in Jaguars lore with his play in the AFC Championship Game after that season. Jack ran down Patriots running back Dion Lewis, stripped the ball as he tackled him, and jumped up and returned it for what should have been a touchdown that gave the Jaguars a 17-point lead early in the fourth quarter. However, the officials blew the play dead after he recovered the ball because they believed he was down by contact.

Replays show he wasn't, and that birthed the "Myles Jack wasn't down" phenomenon. T-shirts, memes, GIFs, and even local craft beers all bear that slogan.