The Canadian came on as a late substitute during the Saints' 3-0 defeat to Kilmarnock at McDiarmid Park on Saturday but lasted only a few minutes before collapsing to the pitch after turning awkwardly.
Saints boss Derek McInnes revealed the 21-year-old is the third player at the SPL club to be troubled by the same problem.
"First and foremost we are hugely disappointed for Marcus," McInnes told the club's official website.
"He will not play again this season and in all likelihood he will return to West Bromwich Albion to carry out his rehabilitation.
"Understandably, he is devastated by the news and our thoughts are with him.
"But he's a young boy and at an early enough stage of his career where he can recover fully from this setback.
"From a St Johnstone point of view it is obviously a huge blow to our options, particularly as Marcus was invariably one of the three under-21 players we are required to have stripped and following on from Kevin Moon and Martin Hardie that is now three players who have suffered this injury.
"However, other players now need to show they can step up to the challenge of replacing Marcus."