Rashford has been nursing a muscle tear on his left shoulder since November, and he has been playing through the pain with the help of injections and painkillers.
It will be interesting to see if the Rashford blow forces Manchester United to dip into the transfer market for another striker now.
The Red Devils have Edinson Cavani as their only reliable goal scorer now, and it could prove to be a bit of a gamble going into the season without signing another goal scorer.
Manchester United begin their Premier League season on the 14th of August, and they will be hoping to go all the way in the competition this season. The Red Devils finished second in the league table last year.
Missing the next 12 weeks welcome as a devastating blow for Marcus Rashford, but the decision to undergo surgery will benefit him in the long run.