The serious nature of the problem only came to light when Green went for scans after complaining of increased pain and he is now set to undergo surgery.
"It came completely out of the blue," said Hull KR coach Craig Sandercock. "It could have happened to me or you.
"He's out for a significant period of time. We're still getting some clarification of that. We're probably still coming to terms with how serious the issue is.
"It could possibly have been life-threatening at one time. It's a serious issue and it's been treated seriously. Our medical staff did a great job in diagnosing him and getting the scans done."
http://www.sportinglife.com/rugbyleague/news/story_get.cgi?STORY_NAME=rleague/12/01/19/RUGBYL_Hull_KR_Nightlead.html&BID=480