5. Kevin Dotson
After three non-descript seasons with the Pittsburgh Steelers, Dotson was traded to the Los Angeles Rams last offseason and followed with a breakout campaign in 2023 (84.3 overall grade from Pro Football Focus; 88.3 run blocking grade-second-best in the league).
If/when Jackson finds green pastures with another team, the Lions will theoretically have money to spend in order to keep their offensive line top-notch. Dotson can play both guard spots, but his performance at right guard last season pushes him more toward being a pivot if Glasgow leaves.
Dotson won't be cheap though, and if not for that he'd be higher on this list.
Update, March 7, 5:55 p.m. ET: According to Jordan Schultz of Bleacher Report, the Rams have re-signed Dotson to a three-year, $48 million deal.
4. Kevin Zeitler
Pro Football Focus pointed to the Lions as a landing spot for Zeitler. Despite being a very good guard for a long time, he just earned his first career Pro Bowl selection in 2023. It's fair to wonder if the Ravens will prioritize other things in free agency, but there have been discussions about bringing him back.
12 years into his career and turning 34 years old right before free agency starts (March 8), Zeitler isn't a long-term solution for the Lions at right guard if Glasgow were to leave. But on a two-year deal, with the idea of drafting someone to take over after that, Zeitler would make a lot of sense.