Castleford Tigers say Luke Gale could miss the rest of the season after he underwent an emergency appendix operation.
The 29-year-old has been one of the catalysts to the West Yorkshire outfit's excellent campaign, scoring 13 tries in 26 Super League games as Cas clinched a first-ever League Leaders' Shield.
The Tigers are already assured of a play-off semi-final berth but may have to continue on their quest to win the Grand Final for the first time in the club's history without Gale.
The England international reported feeling pain on Monday before being taken to hospital on Tuesday where he underwent surgery, putting his participation in the remainder of the campaign in serious doubt.
"I'm absolutely gutted to be facing surgery at this point in the season," said Gale, who is also now a doubt for England's World Cup campaign.
"This is a freak situation that could happen to anyone at any time and it's just really unfortunate for me that it has happened to me now at such a crucial point in the season.
"Rest assured I'll be doing all I can to aid my recovery with an aim to getting back on the pitch as soon as possible.
"In the meantime, I'll be 100 per cent behind my team-mates in our quest for the Grand Final to top off what has already been a fantastic year."