Takapuna manager Glenn Gissing said the team was reeling from Mr Halaifonua's collapse.
"It's still early days, it's just a waiting game now. Whether he will come out of the coma, they don't know. It's most concerning. We're all hoping and praying for him," he told the Herald.
"He collapsed at the end of the game. I was walking back to the clubrooms with all the gear, the game had finished and everyone was shaking hands and Willie just dropped to his knees. Willie had just been made our player of the day. He played very well.
"He had a couple of knocks during the game. He had a head clash with a Massey player but Willie was okay so he obviously carried on playing. There was another incident right at the end, in the last five minutes of the game, and it wasn't deliberate, where a stray knee hit him in the head. That probably compounded the first knock."
Mr Halaifonua showed no indication of suspected concussion.
"There was no sign there was a problem at all," said Mr Gissing.
"Then he has completely collapsed. He was out for the count. It wasn't a very nice thing for the boys to see."
The injured player's family were at his bedside last night and their church minister had also visited the hospital.
"His mother was there. She apparently doesn't normally go to the games. Then, the day she comes along this happens," Mr Gissing said.
"Now, there is every possibility he might not ever be able to play again. We just don't know what damage has been done to his brain. It's pretty damn serious."
Massey head coach Brent Semmons said Mr Halaifonua's collapse was frightening.
"My captain is feeling guilty because he hit him in a tackle near the end of the game.
"He's just got so much guilt about it, but I said to him 'Mate, you can't do that'.
"Rugby is a collision sport and we put ourselves in that position for the game, but obviously not to that extent.
"All the boys are praying for him. We are all concerned."
An email sent to Mr Halaifonua's teammates last night said club management, the North Harbour Rugby Union and the New Zealand Rugby Foundation were supporting his family.
"I would ask you to keep Willie [and his family] in your thoughts and prayers as they go through the challenges that lay ahead of them," wrote club chairman Simon Cheesman.
Concussion rules
* In accordance with International Rugby Board rules, any player thought to have suffered a "suspected loss of conciousness" must be referred to a doctor for apitchside suspected concussion assessment (PCSA)
*They are referred for the test if they are unsteady on their feet, if they are disoriented or confused, if they appear dazed or are exhibiting inappropriate behaviour or other symptoms or signs suggesting a suspected concussion.
*Players can only go back on the field if the person administering the test deems them fit to play.