Corsie was stretchered off following a second-half foul on Spanish striker Veronica Boquete, the player whose 122th minute goal enabled Spain, and not Scotland, to qualify for next summer's finals in Sweden.
The injury, an anterior cruciate ligament tear, is almost identical to the one sustained by her Scotland central defender partner Ifeoma Dieke playing for Team GB at the Olympic Games. The Glasgow City player has the additional complication of a meniscus (cartilage) tear in the injured left knee.
"It will definitely need surgery of some kind," confirmed Corsie. "Realistically, I am going to be out for nine months because it's not just the ACL. If we had qualified for the Euro finals it's unlikely I'd have been fit in time. The next nine months are going to be very difficult because football has been a huge part of my life for so long."
The Aberdonian will miss Glasgow City's final league match, away to Spartans on Sunday, and also the Scottish Cup final against Forfar next weekend.
Corsie, an accountant, expects to be off work while she is recovering from her operation, but added: "Once I'm able to get into the office, I'll be able to work as usual."
The tackle on Boquete resulted in a yellow card from German referee Bibiana Steinhaus after the game had been held up for three minutes to allow Corsie to be treated and stretchered off. "Some of my team-mates thought I was milking the injury to get out of the booking," she said.
After being treated in the dressing room and given a brace and crutches, Corsie returned to watch the 30 minutes of extra time after the teams had drawn 1-1 in regulation play.
"What happened was so unfortunate," she said. "If somebody had said at the start that would be the outcome, nobody would have believed it. The last few minutes were crazy and it was absolutely devastating when that ball rolled into the bottom corner for their winner, followed by the final whistle. I don't want to blame the referee, but two extra minutes being added on when there seemed no reason for it makes it even harder to take."
Team-mate Dieke will see a consultant in March, and hopes to be given the all-clear to resume playing.
Scotland coach Anna Signeul said: "The only positive thing you can say is that Ifeoma and Rachel are two very dedicated players who will do absolutely everything in their powers to get back.
"You have a bigger risk of an ACL injury if you are a woman. No matter how much women train, they can't get the same muscle mass to protect the knee as men can."