Hull scrum-half Sean Long could miss the rest of the season with the dislocated shoulder injury he suffered in Sunday's derby defeat by Hull KR.
The 34-year-old former Great Britain star, who suffered the injury while making a tackle on Ben Galea, has now been sidelined for three months.
And, if Hull miss out on the play-offs, Long will struggle to be back before the league season ends on 9 September.
"Sean will face at least 12 weeks in rehabilitation," read a Hull statement.
"Initial examinations from a specialist didn't deliver the worst possible news, but he still requires surgery.
"It does mean he has an outside chance of returning before the end of the season, especially if Hull reach the play-offs. However, it will certainly be a race against time to get him fit."
The luckless Long was making his first appearance since breaking his thumb in April, also on derby duty against Rovers.
He was taken after the game on Sunday to hospital, where he had his shoulder popped back in. But, after seeing a specialist on Monday, the club have now had the chance to assess the full extent of the injury.
"He's had a tough time with injuries this year," said coach Richard Agar. "He was in a lot of pain."
Long has endured a frustrating time with injuries, having made just 22 appearances since making the switch across the Pennines for the 2010 campaign following 12 glorious seasons with St Helens.
He missed two games this season after being sent off and consequently banned by the Rugby Football League for striking Castleford's Jake Emmitt in their Super League meeting in April.
And, as well as enduring hamstring and knee problems, he faced a similar fight to be fit at the end of his first campaign at the KC Stadium, when he missed six matches with a dislocated elbow.
Long is out of contract at the KC Stadium at the end of the season. But Agar said on Sunday that Hull "owed" it to the player to allow him to recover before deciding his future.
Long insists that he has not given up hope of playing for the club again this season.
"I'm hoping I can get a few games at the end of the season like I did last year," he said. "I certainly haven't given up hope of pulling on that black and white shirt once more.
"I feel devastated. I feel like I've let the Hull fans down and let down my team-mates and the coaching staff.
"Hull signed me in good faith and I know the fans were looking at me to have a big influence on the team so I'm disappointed for those fans who wanted to see me play."