What the heck happened?

That was the most logical reaction to the photos Antonio Brown recently posted to Instagram showing blister-like abnormalities on the bottoms of his feet.

Well, details regarding the Oakland Raiders wide receiver’s “injury” have begun to emerge.

ProFootballTalk’s Chris Simms reported earlier this week, citing someone with knowledge of the situation, that Brown burned his feet by entering a cryotherapy machine without the proper footwear, resulting in frostbite.

A source confirmed to ESPN on Wednesday that Brown’s mysterious foot injury indeed is the result of extreme frostbite caused by a cryotherapy machine, and NFL Network insider Ian Rapoport added that the seven-time Pro Bowl selection is considered day-to-day.

“As far as the backstory — what led to this — what I was told, talking to a couple Raiders people, basically the story that they are saying is that Antonio Brown used a cryogenic chamber without proper footwear and that is why his feet ended up the way they did,” Rapoport said Wednesday on NFL Network’s “Inside Training Camp Live.” “Certainly, some other questions medically, for his feet, how they ended up looking like that, how he trained through feet which are so badly injured he really can’t continue to train. A lot of questions there. But at the very least, that is the story they are saying. Still day-to-day. Unclear when Antonio Brown is going get back out at practice.”

Brown, who was acquired in a trade from the Pittsburgh Steelers this offseason, has missed a significant part of his first training camp with the Raiders. According to ESPN, the 31-year-old hasn’t practiced since July 30, when he left the team to visit a foot specialist.

It’s unclear at this point when Brown will return to the gridiron, although ESPN’s Adam Schefter reported over the weekend the injury is not believed to be a long-term issue.

Brown, one of the best wide receivers in the NFL, is coming off a 2018 season with the Steelers in which he caught 104 passes for 1,297 yards and an NFL-high 15 touchdowns. He totaled at least 1,200 receiving yards in each of the past six seasons.