Antonio Brown just issued a massive apology for his off-the-field behavior -- but there's one huge problem with his mea culpa ... it's unclear what he's specifically apologizing for.

"First and foremost, I’d like to apologize to my family, friends and anyone who I offended," Brown said on IG.

"I never once meant to make anyone feel like I wasn’t thankful and appreciative of the opportunity that I was afforded to play the game I love."

Here's where things get even murkier ... AB references "inexcusable" behavior -- but doesn't specify if he's talking about serious allegations like rape or stupid incidents like farting on his trainer.

"While my behavior was inexcusable, sometimes when people are coming at you with false information and allegations, we handle ourselves in ways that we sometimes regret."

Our takeaway from that line is that AB is referencing the menacing text messages he sent to a woman who had accused him of sexual misconduct.

The Patriots cut AB after they learned about AB's texts and the NFL has launched an investigation.

"I do take full responsibility for my actions and I’m working everyday to repair what I broke."

Brown then turns his focus on getting another shot in the NFL ...

"I do know that if I’m ever given the opportunity to play the game that I love, I’m going to work extremely hard to show the world how much I appreciate another chance."

"To the organizations that I offended, I offer my sincere apology to you and my hope is that you forgive me and help me move on from this minor setback."

Those organizations could be anyone from the Patriots to the Oakland Raiders to the Pittsburgh Steelers ... maybe even the Buffalo Bills.

As we previously reported, the Raiders had signed AB to a 3-year, $50 mil contract ... but he had drama with his helmet, his feet and had public spats with the GM and coach Jon Gruden.

The Patriots picked him up ... only to dump him right after the text message incident. Brown later bashed the Pats on social media and referenced owner Robert Kraft's prostitution scandal.

The Steelers couldn't wait to dump AB after he live-streamed a private locker room conversation ... and he went after QB Ben Roethlisberger in the media.

As for the Bills, there was interest in signing AB ... but he reportedly refused to play there and a potential trade never went through.

For his part, AB has been training like a maniac over the past few months -- and you gotta wonder if there's real interest from an NFL team looking to beef up the WR position before the playoffs.