Oakland Raiders wide receiver Antonio Brown might have come up with a new reason to miss training camp: frostbite.

The issues that have kept the star wideout from the practice field since July were thought to be blisters, with Brown posting a photo on social media on Monday showing skin peeling from his feet.

Antonio Brown shows off his blistered feet on his Instagram story. Photograph: Instagram

But Chris Simms of PFT Live reported that the photo shows burned feet as a result of Brown entering a cryotherapy machine without the proper footwear. A source confirmed the report to ESPN on Wednesday.

Raiders coach Jon Gruden told reporters that Brown, a seven-time Pro Bowl selection with the Pittsburgh Steelers before his offseason trade, wasn’t at the team’s camp in Napa, California, on Tuesday.

Gruden added that the team is “gathering information” but otherwise declined to comment on the situation, including whether Brown would be able to make his Raiders’ debut when the team opens the regular season on 9 September against the visiting Denver Broncos.

Brown, 31, has been one of the league’s most prolific players. He was an All-Pro four straight years from 2014-17 and is the first player with at least 100 catches and 1,200 yards receiving in six straight seasons. His 686 catches and 9,145 yards since 2013 are the most for any player in a six-year span.

But despite that production, he wore out his welcome in Pittsburgh and was acquired by Oakland in March for picks in the third and fifth round of the 2019 draft.

Drew Rosenhaus, who represents Brown, did not immediately respond to a request for comment from the Guardian.