NFLers wringing their hands over Friday night's game in Brazil need to relax ... 'cause Gilbert Burns -- a UFC superstar who's from Rio De Janeiro -- tells TMZ Sports the athletes are going to be just fine in his native land.

The issue has become quite the talking point ever since the NFL announced the Eagles would take on the Packers in a São Paulo season-opening showdown -- especially after Philadelphia corner Darius Slay blasted league officials this week for planning the contest in a place with a reported high crime rate.

But, when we spoke to Burns about what the guys can expect when they finally touch down in South America -- he said it straight up will NOT be "that crazy."

He explained that like a lot of American cities -- it has its bad areas ... but for the most part, it's "beautiful."

In fact, he encouraged the players to spend their free time touring the town.

"Those guys -- all the football players -- they look like Brazilians a little bit," the 38-year-old Brazilian fighter said. "They're big, they're strong. So they're not going to have any problems there. And they're going to have a lot of fun."

According to Slay -- who ended up backing off his Brazil comments in a post on X on Wednesday -- the NFL has advised players to stay in their hotels during the trip. But Burns says the UFC has sent similar memos when its athletes have fought in Brazil, and he's said the ones who've ignored it haven't regretted it.

As for the notion that wearing the color green might cause problems ... Burns says he's never heard of anything like that.

"It's very nice," he said.

Burns will fight this weekend in Nevada against Sean Brady and he's expecting a good show -- but if he wasn't slated to be in the Octagon ... he told us he'd be right there in São Paulo catching all the action.