It's understood the incident occurred earlier this week.
The publication reported it was Smith Shields right knee which was injured, with the recovery time sitting at anywhere between six and nine months.
An official statement from the Raiders has ruled the 22-year-old, who has made nine NRL appearances including seven last year, out for the season.
"In disappointing news, Harley Smith-Shields will miss the 2022 NRL season after suffering an ACL injury," the statement read.
"Smith-Shields suffered the injury at training on Wednesday.
"He will meet with a surgeon to determine a date for surgery and begin his rehabilitation post-surgery."
Given the fitness questions around Jarrod Croker and departure of Bailey Simonsson (which was offset by the arrival of Nick Cotric), the injury to Smith-Shields puts a dent in the Raiders' backline depth, should they suffer injuries or a lack of form throughout the season.
Coach Stuart told The Canberra Times that there was no collision causing the injury.
"I don't know if I've been as disappointed for a player as I was yesterday when we heard the snap," Stuart said.
"There was no collision, it was just the way he turned and you could hear the ACL snap. It was sickening.
"I don't think I've ever been as disappointed for a young player as I was yesterday because Harley had had his best off-season to date and was going to continue the start of his NRL career."
The Raiders will take on the Cronulla Sharks in Round 1, and Stuart said he was likely to be in the team.
"He most definitely would've been one of the outside backs. That's how confident I am through his performance right throughout the off-season," Stuart told the publication.