St Helens half-back James Roby lost five kilos in weight after being hospitalised by a virus that forced him to miss the win over Huddersfield. The 20-year-old could return to face Bradford on Friday, but Saints coach Daniel Anderson said the youngster still "looked very washed out".
Anderson added: "He lost five kilos and that does knock you a little."
Scrum-half Sean Long and prop Jason Cayless should be fit to play while James Graham returns from suspension.