Luke Walsh is out for the season after undergoing surgery on a broken leg - while fellow Saints star Jon Wilkin also faces an indefinite absence.
Saints coach Nathan Brown revealed that Walsh, 27, who has starred in the red vee when fit this year, suffered a broken fibula against Widnes last weekend and will be out for “four or five months”.
Wilkin, 30, an option in the halves in Walsh’s absence, remains out with a shoulder injury with no firm return date set.
Brown said: “Walsh has snapped his fibula and has already had surgery - with plates and bolts put in. He’ll be out for four or five months. Given the type of injury it is, it’s about as good a result as you could expect - it could have been worse.
“Jon Wilkin is an unknown, to be honest. We’re not sure whether he will appear again this year or not. He hurt his shoulder against Salford and it’s an ongoing issue but we’ll see what unfolds in the next couple of weeks.
“You can put a player out for surgery and he’s definitely out or you can try to solve the issue through rehab and that’s what we’re trying to do. He had the same issue a couple of years ago too.”
In the absence of Walsh and Wilkin - and with Lance Hohaia still several weeks away from a return to the fold - Gary Wheeler and Jordan Turner are set to be given the opportunity to play alongside each other in the halves.
The pair impressed in the playmaking roles after Walsh was stretchered off against Widnes.
Brown said: “We’ve had people step in throughout the year - Luke’s missed a number of games that we’ve done well in and come off in a number of games we’ve won too. We’ve all just got to bind together and do a good job.
“At the moment our best option appears to be Jordan Turner and Gary Wheeler. Jordan’s done a great job for us there when he’s had the chance so, at this stage, we’re planning to keep Wello at full back. Jordan trained there a lot in pre season too.
“Wheeler’s a fine young player too, so it’s the most stable option. Jordan and Wheels both kick the ball well and Robes is a terrific kicker too - he just never really gets the chance.
“We’ve had to make some slight adjustments to the way we play because of injuries in the back line - it just adds a bit more responsibility across the board. Structure-wise there’s some things we won’t do now that we did do with different halves but there’s plenty that we’ll still do.
“We know it won’t be perfect but if we all work together as a group we’ll give ourselves the best shot each week.”