Full back Jack Welsby damaged his shoulder in the act of scoring the try that gave Saints a toe-hold in the game at Warrington.
The away crowd feared the worst as they watched on as Welsby was led off by the club doctor.
And those initial fears were confirmed by head coach Paul Rowley after the game.
Rowley said: “Jack was struggling there with a shoulder injury and has gone off to hospital.
“Unfortunately, I think that is going to be in the Matty Lees category so we have got a couple of our biggies missing for the foreseeable.
“So that is another challenge for us.”
Centre Nene Macdonald switched to full back for the remainder of the game and he is an option going forward for what is likely to be a significant lay-off.
Rowley explained that whatever happens will not be a repeat of last year’s chopping and changing in the spine.
“It is a different situation to last year,” he said.
“Last year was about trying to find a combination – this year is about solving a problem that has been presented to us by injury.
“So it is totally different. “I have got options – Tristan can play there and Nene can play there so I will work that out in the week.”
Saints also could switch Harry Robertson to full back.
Saints lost the game 24-14 after trailing 18-0 at the break