Simone Biles may be a beloved Olympic champ, but NFL fans say she's not above the sport's rivalries ... roasting the Olympian for wearing a Packers jacket to a Bears game.

Here's the deal ... Biles' husband Jonathan Owens made the switch from the Green Bay Packers to the Chicago Bears this offseason -- two teams locked in one of the oldest rivalries in the sport.

It seems at some point last year -- the one season JO played for GB -- Simone bought a custom black and white jacket featuring action shots of Owens on the Packers ... with the iconic "G" logo on her shoulders.

Biles wore the jacket to the Bears' preseason game Saturday against the Cincinnati Bengals -- clearly just trying to show love for her man ... but, fans online aren't happy about it.

NFL stans are telling Simone she needs to get rid of the jacket ASAP ... saying the rivalry is much bigger than she realizes.

Simone and Jonathan married last year a week before he signed with Green Bay ... and, Simone was spotted at multiple games last year cheering on her dude.

He returned the favor this summer ... negotiating his contract with the Bears so he could go watch Biles at the 2024 Paris Olympics -- where she won three gold and one silver medal.

As for her fashion choice ... seems most people are leaving her off the podium.