Marcus Smith's hopes of stepping out of Owen Farrell's shadow in the Six Nations have got off to a frustrating start, with the exciting England five-eighth ruled out of his side's opening match of the tournament.
England are waiting for a second opinion on the scan before confirming a return date, raising the possibility Smith could miss additional matches.
The 24-year-old was the favourite to start the match in place of fellow five-eighth - and former captain - Owen Farrell, who has been deemed ineligible for selection following his move last week from Saracens to French club Racing 92.
Farrell had already made himself unavailable for this season's Six Nations to focus on his mental well-being and Smith was a leading contender to fill his boots.
Now that honour will go to George Ford or the uncapped Fin Smith.
"He's not fit for this weekend," assistant coach Kevin Sinfield said.
"It just happened in training, the early part of the session. Just one of those things.
"The boys have had two days off (for) recovery and Marcus, being the bundle of energy that he is, was doing his thing.
"Unfortunately these things happen. We are gutted for him because he's been amazing to work with and we hope it will not be too long."
England coach Steve Borthwick will name his starting line-up on Thursday.