The former Liverpool youngster damaged the muscle away at Peterborough last month, only a few weeks after making his comeback from a separate hamstring issue he suffered earlier in the season.
Brewster was initially assessed and a number of treatment options were considered, with the player himself heavily involved along with United’s medical staff and specialists.
And a decision has been taken for Brewster to go under the knife tomorrow, a day before the Blades take on West Bromwich Albion at Bramall Lane as they bid to close the gap further on the Championship play-off places.
“He’s having an operation tomorrow, which will rule him out probably for the season,” Heckingbottom said today.
“If he’s back before, then it’s a bonus but we’re not counting on it. We’re going to help him through it.
“He’s got his head around it and been part of the decision-making process. It’s not the same injury, it’s totally different and needs different treatment.
“He’ll work hard to come back fitter and stronger, as he did last time. He was in a good place, his fitness levels were high, and we’ll want the same for him when he comes back next time.”
Brewster had scored twice in three games when he suffered his first injury against Bristol City, in Heckingbottom’s first game in charge. Brewster then scored against Luton in front of the Kop after returning, but damaged a hamstring again in the next game at Peterborough’s London Road.
“You want to give them the support,” Heckingbottom added, “but injuries are part and parcel and we don’t want to wrap people in cotton wool so they can’t see how tough this industry is.
“It’s happened and we’ll help him through it. His rehab will all be laid out for him, we’ll get involved in tactical stuff at the back end, and we may do some analysis work with him as well.
“So there’s a lot we can do with him to develop him and give him ownership of his role in the team and his development.”