Hecher was a second-half substitute in Saturday's 1-0 win over Western Sydney but was forced off with her ACL injury in stoppage time.
She will have knee reconstruction surgery on Wednesday.
"I knew straight away when I went on the ground that it was it," Hecher said in a club statement on Tuesday.
"I was pretty upset, but everyone has been amazing and very supportive which does help you to get in good spirits.
"I know they're going to be wearing the jersey for me even more now that I won't be playing and they're supporting me in every single way."
Hecher, 30, previously tore her ACL while playing in Brazil in 2011 and planned to draw on that experience.
"It's a mind game, you try to keep yourself positive as much as you can, there will be days that will be hard but you see the bigger picture that you want to come back stronger, you want to come back and help the team," she said.
"I feel like I'm letting the team down this year but all I can do now is be there for the girls for the rest of the season to support them in the way that I can."
Brisbane sit sixth in the league, with two wins, one draw and two losses.
23°C