The Raiders' 1st round draft pick as been in the hospital for the past week due to an abdominal issue. The rumor is that Hayden has undergone a "procedure" (read: surgery) to remove scar tissue in his chest from the surgery that saved his life in November of 2012.
It is being reported that he will miss the rest of offseason activities, but there is no indication this will cause him to miss training camp.
Hayden tweeted on May 20th that he was experiencing stomach pain
This is huge NFL news because of how it relates to the safety of the game, this was a big story in the NFL draft and this is a high 1st round draft pick.