St Helens coach Daniel Anderson has admitted that skipper Paul Sculthorpe is still some way off match fitness.
Sculthorpe joined Saints from Warrington in 1997
The former Great Britain captain, 30, has been hit by injury for two years and has not played since June after rupturing an Achilles.
"His rehab is not going as rapidly as it was last month," said Anderson.
Saints have also been hit by the news that Jon Wilkin (knee ligaments) and Maurie Fa'asavalu (broken thumb) are likely to be out for six weeks or more.
Centre Willie Talau (calf) will also miss the derby with Warrington on Friday, but he is expected to return the following week.
We were healthy two weeks ago and crowing about it, but that's the way it goes
Sculthorpe's absence is more of a concern, with Anderson admitting: "He's hit a bit of plateau."
The forward had surgery on his ruptured Achilles in the autumn but has been unable to return to action as quickly as he had hoped.
"He can't do anything dynamic," Anderson said. "He's still running but he's been stuck at 75-80% for a couple of weeks and can't come in the team until he's 100%."
Teenage trio Chris Dean, Gareth Frodsham and Kyle Eastmond, who have a combined Super League career of three matches between them, have been added to the squad.
"We've had a few setbacks," Anderson said. "We were healthy two weeks ago and crowing about it. But that's the way it goes."