Miller hobbled off after 19 minutes and coach Chris Chester said: “It doesn’t look great.
“The medical people are hopeful it’s just a medial ligament, similar to the injury he sustained a couple of years ago.
“If it is just the medial, it’s probably a four to six-week injury.”
Miller’s departure made a difficult task that much tougher for Trinity, who were already without several players including star winger Tom Johnstone, but they competed well in the opening 40 minutes and there was no scoring at the break.
Wakefield have made a habit of fading after half-time this season and that was the case again as they conceded six tries before Jay Pitts went over for a late consolation, improved by Mason Lino.
Chester reflected: “The effort’s not in question, but what we questioned in the dressing room is what’s going on between the ears.
“We put in a big performance in that first half, then we came up with some really poor lapses in concentration.
“It is so frustrating. I know the guys are hurting, but we’ve got to be smarter with the personnel we’ve got.”
Saints went ahead through Kevin Naiqama 90 seconds into the second period and Wakefield were 18-0 adrift by the 52nd minute, after James Bentley and Jack Welsby had also touched down.
Regan Grace, Naiqama and Grace again added to Saints’ haul, Tommy Makinson kicking four conversions and Lewis Dodd one, before Trinity’s late consolation score.
Saints coach Kristian Woolf said: “Even though Wakefield had a lot of ball, I didn’t think they were going to score.”
St Helens: Coote, Makinson, Naiqama, Welsby, Grace, Lomas, Fages, Walmsley, Roby, Paasi, Thompson, Bentley, Joe Batchelor. Substitutes: McCarthy-Scarsbrook, Amor, Dodd, Wingfield.
Wakefield Trinity: Hampshire, Senior, Lyne, Arundel, Kershaw, Miller, Lino, Fifita, Crowther, Arona, James Batchelor, Pitts, Westerman. Substitutes: K Wood, Green, Battye, B Walker.
Referee: J Child (Dewsbury).
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