St Helens' Australian scrum-half Luke Walsh has been ruled out for four to five months with a broken leg.
The 27-year-old spent two nights in hospital after sustaining the injury in the first half of last Friday's 44-22 win over Widnes and has already undergone surgery.
Although Walsh's first season in Super League has been cut short, the injury was not as serious as initially feared.
"He's basically snapped his fibula," St Helens coach Nathan Brown said.
"He's had surgery with the plate and bolts and all the type of things that go in and he'll be four or five months.
"It was as good a result as you could expect. It could have been worse."
The loss of Walsh is still a body blow to the Super League leaders, who are just two points ahead of Leeds going into the last five games of the regular season.
The former Penrith half-back, who joined Saints on a two-year contract, scored 66 goals and 153 points in his first 15 Super League appearances and was making his return last Friday from a three-match absence with a back injury.
With fellow half-back Lance Hohaia ruled out for another five weeks with a foot injury and full-back Jonny Lomax (knee) and loose forward Jon Wilkin (shoulder) also sidelined for lengthy spells, Saints will be without a host of key players for the run-in.
"It's happened," Brown added. "Luke has missed a number of games and we've had people stepping in through the year. We've all got to bind in and pull together and do a good job.
"He's done and dusted so we've got to look at the people we've got to play there, that's probably the key for us moving forward."
Brown has the option of switching skipper Paul Wellens into a playmaking role, especially with former Hull full-back Shannon McDonnell available to make his debut, but he is set to start Friday's game at Hull with Jordan Turner and Gary Wheeler after they finished the Widnes match at half-back.
"At the moment that would appear to be our best, most stable, option," Brown said.
"They both played there last week. Gary has played a number of games earlier in the year in that position and Jordan has filled in a couple of times this year and done a great job. He's also played there a number of times for Hull."