Lions linebackers had a 2016 season that was rather nondescript. They finished with no sacks, no forced fumbles and no interceptions. Even for a more passive scheme, that's a lack of impact that raises major concerns entering the offseason.
Joshua Bynes is a free agent, and neither of the other starters exactly have security for next season, let alone the future. DeAndre Levy has ongoing durability questions, and Tahir Whitehead might do well with a move back to outside linebacker. Either could be potential cap casualties.
One offseason is probably too short of time to find three new starters, but the search for long-term fits begins now.