UFC heavyweight champion Jon Jones was already a big favorite to defeat Stipe Miocic. Now he's a massive one.

When the odds were released for the UFC 309 main event after it was officially booked last month, Jones (27-1 MMA, 22-1 UFC) opened as a -410 favorite and Miocic (20-4 MMA, 14-4 UFC) a +320 underdog via DraftKings on Sept. 16, but those odds have drastically changed in the past month to make Jones a massive favorite, with DraftKings currently listing Jones -550 and Miocic +410.

Those odds are even wider at two other prominent online sportsbooks, FanDuel and BetMGM. FanDuel lists Jones -620 and Miocic +400; BetMGM has Jones as a whopping -700 favorite and Miocic +500. The major shift in Jones' favor indicates that public money has come in heavy on the champ.

Perhaps Miocic's age and inactivity are the reasons why. The former UFC heavyweight champion, now 42, hasn't competed since March 2021 when he lost the title to Francis Ngannou by vicious second-round knockout.

Jones, 37, has competed just once since February 2020. The former longtime light heavyweight champion debuted at heavyweight and submitted Ciryl Gane to win the title vacated by Ngannou in March 2023. Jones is returning from a torn pectoral that canceled the originally scheduled fight with Miocic last November at UFC 295.

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For more on the card, visit MMA Junkie's event hub for UFC 309.

This article originally appeared on MMA Junkie: UFC 309 odds: Jon Jones swells to massive betting favorite with Stipe Miocic fight one month away