The striker took part in the warm-up and lined up for the national anthems, but just as Norway were breaking from their huddle, Hegerberg headed quickly down the tunnel to the locker room.
Hegerberg was replaced in the starting line-up by Sophie Roman Haug (24) as Norway sought to bounce back from their 1-0 defeat by co-hosts New Zealand, but the game finished 0-0.
"She (Hegerberg) felt a tightness during the regular warm-up, which she felt was going to be alright going into the game," Victor Bernard of Hegerberg's representatives AV Sports told Reuters in an email exchange.
"But as she sprinted after the usual anthems and handshakes - she always gets a couple of sprints going before the team photo - she felt the groin becoming tighter.
"She told the staff instantly that it would be better to have someone at 100% on the pitch to play the game, which is something that hasn't been caught on camera.
"She genuinely thought she could play the game before having those couple of sprints," Bernard explained.
Hegerberg's sudden withdrawal caused a flurry of online rumours, with theories from illness to a fall-out with the Norwegian coaching staff circulating.
However, she opted not to play solely due to the discomfort she felt in her groin, Bernard said.
"Ada would never refuse to play at such late notice, she's not the type of player who'd put her team at risk. She felt playing would potentially take her out of the World Cup while there is still at least a game to play," Bernard said.
"She genuinely did not know how to proceed, and to prevent the team from losing a substitution, she headed to the locker room, where she received treatment quickly after."
Bottom of Group A with one point from their opening two games, Norway hope that Hegerberg will be fit for their final group game against the Philippines on Sunday, while leaders Switzerland take on second-placed New Zealand.
