Improper footwear is apparently the source of Antonio Brown's foot injury.
NFL Network's Ian Rapoport confirmed the cause of Brown's injury Wednesday:
Rapoport had also reported Sunday that Brown visited a foot specialist and is day-to-day with the injury.
Raiders head coach Jon Gruden confirmed the team was "gathering information" about Brown and that the seven-time Pro Bowler isn't at training camp, per Scott Bair of NBC Sports Bay Area.
Fans knew something was wrong when Brown shared a photo of his feet in an Instagram story:
While the circumstances of his injury are unusual, the effects can be serious. Manny Harris saw his NBA career derailed when he suffered freezer burn after he wore wet socks during a cryotherapy session.
Brown doesn't seem to be in danger of a similar fate, but somewhat worryingly, Bair noted Gruden "refused to speculate on his readiness" for Oakland's season opener against the Denver Broncos on Sept. 9.
The Raiders are counting on Brown to play a key role in 2019. He had 104 receptions for 1,297 yards and an NFL-best 15 touchdowns a season ago, and his presence should be a massive lift to Derek Carr after the quarterback struggled in Gruden's first year back on the sideline.
The fact that Brown has already missed time with which he could build an on-field rapport with Carr is one thing. It's another if the receiver's injury jeopardizes his availability to start the regular season.