Heffernan, who missed the opener against the Mainland Tactix on Sunday, hurt her knee at training last week but is expected to return this season.
Steel physio Stacey Allan said there was a robust recovery plan and Heffernan was making "positive progress" as they worked towards her return.
While disappointed, Heffernan said her focus was on getting back on court.
"Unfortunately, injuries are one of the realities of elite sport, but that doesn’t make it any less heartbreaking not to be able to get out there with my team," Heffernan said.
"We have all worked incredibly hard during the preseason and deserve to reap the rewards of that now the competition has started.
"Watching from the sidelines definitely fuels my determination. I will be following the expert advice of our medical team to the letter and doing everything in my power to play as soon as I get the green light, but I know I have to be patient."
The Silver Fern travelled to the Steel’s opening game in a leadership role.
"Naturally I want to be out there playing my part, but I have the utmost faith in our entire squad to get the job done regardless of who is wearing the bibs."
The Steel head to Hamilton to play the Waikato-Bay of Plenty Magic on Monday.
