According to Shutdown Corner's Liz Roscher, the injury was serious enough to require surgery, so Harbor told Becca Kufrin he'd have to leave the show:
Harbor has spent seven years in the NFL and was under contract with the New Orleans Saints in 2017. He didn't appear in a game for New Orleans, though, after the team placed him on injured reserve last August.
Harbor tweeted Monday night he's looking to continue his football career:
If Harbor is unable to find a team in time for the start of the 2018 season, then maybe he can position himself as the next star of The Bachelor.