The 27-year-old is the sixth defensive lineman to either opt out, go on injured reserve or retire since July 31. Lynch's retirement comes one day after veteran end/tackle Rodney Gunter said he was stepping away from the game because of a heart problem.
"The one thing I think I've learned over the history of this league is even though you're doing all these moves or you're doing all these things to fix things and you feel comfortable, at any moment in time those things can change," Jaguars coach Doug Marrone said during a Monday morning news conference. "And you've got to be prepared and you've got to be able to do it. I know that there will be a lot written about, kind of like you said, these plans that they have, have been blown up. But it's also a great opportunity and a great challenge for these other guys to step up, and if you have that happen, that's great. Especially the young guys.
"The guys that we're talking about [that are not available] were guys that were experienced, guys that have done it before. Having those veteran type of guys brought in, we still have a decent mix, but now it's a little bit more on the younger guys and guys that have been here to step up."
Lynch had 20 sacks over six seasons with the San Francisco 49ers and Chicago Bears. He signed a one-year contract worth $1.01 million with the Jaguars in March. He is Jacksonville's third free-agent signee who won't be playing this season.
Tackle Al Woods, who signed a one-year deal in March, opted out because of the coronavirus. Gunter had signed a three-year deal worth $18 million. Woods and Gunter were signed as replacements for Marcell Dareus and Calais Campbell.
The team declined to pick up Dareus' 2020 option, a move that saved the team $19.5 million. The Jaguars traded Campbell, who was due to make $15 million and count $17.5 against the salary cap this season, to the Baltimore Ravens in March for a fifth-round pick that the team used to take Auburn safety Daniel Thomas.
End/linebacker Lerentee McCray also opted out because of the coronavirus. Tackles Dontavius Russell (hip) and Brian Price (knee) were placed on IR, though Price received an injury settlement and was released on Monday.
DE Yannick Ngakoue has not signed his franchise-tag tender and has not been at training camp, though he has had several conversations with Jacksonville general manager Dave Caldwell since firing his agent last week.