Ragnow had been under contract for two more seasons after the Lions exercised their fifth-year option on his deal last week.
The 24-year-old Ragnow is entering his fourth NFL season after being drafted in the first round out of Arkansas in 2018. He has started all 45 games he has appeared in and earned his first Pro Bowl berth last season.
He ranked fourth among qualifying centers in run block win rate and seventh in pass block win rate last season, according to ESPN Stats & Information.
The Associated Press contributed to this report.