The Detroit Lions will certainly be considered one of the top NFC teams to beat next season when the NFL kicks off again, but Dan Campbell's group will have a different look up front on offense after one of its biggest stars surprisingly retired on Monday.

Detroit Lions All-Pro center Frank Ragnow is retiring from the NFL after seven seasons in the Motor City. The 29-year-old on Monday announced his retirement from the league via a post on Instagram . Ragnow did not participate in Detroit's OTAs last week.

DETROIT — Detroit center Frank Ragnow, a 4-time Pro Bowl selection who was key to coach Dan Campbell's Lions revival, announced his retirement from the NFL on Monday after 7 seasons. Ragnow, 29, posted to social media that he has tried to convince himself he's feeling well enough to play, “but I'm not,” he said.