Burleson spent four seasons with the Lions, but Detroit likely made this decision with financial flexibility in mind. The 32-year-old Burleson caught 39 passes for 461 yards and a touchdown last season in nine games. He missed time after injuring his arm in a car accident.
The Lions drafted Delmas in the second round in 2009, and he's been a consistent starter for them since then. If Burleson and Delmas don't return to Detroit under different contract terms, the Lions will have significant holes to fill at both receiver and in the secondary.
"The last 4 years in Michigan been incredible!" said a message on Burleson's Twitter account Thursday. "MY TEAM, FANS & the CITY will missed more than you know! Thank You!"
When healthy, Burleson was a productive complement to star receiver Calvin Johnson. Now the pressure will be on Detroit's other receivers to step up. Ryan Broyles has been limited by injuries, but Kris Durham caught 38 passes for 490 yards last season, so perhaps he could fill a bigger role in 2014.
Delmas started 15 games last season and finished with a career-high three interceptions. It looked like Delmas might leave the Lions last off-season, but he agreed to stay with Detroit on a two-year contract.
Safety Glover Quin started all 16 games for the Lions last season, but none of the other safeties on the roster have much experience in major roles.
The popular Burleson caught 194 passes in his four seasons with the Lions, including a career-high 73, when Detroit made the playoffs. That was also the last time he played a full season.