Wainui (25) died near Tauranga in the Bay of Plenty last Monday morning.
He was farewelled on Sunday at Te Wainui Marae in Gisborne.
This morning Coroner Louella Dunn confirmed to the New Zealand Herald that his death "is being treated as a suspected suicide".
She has made interim suppression orders around the circumstances of Wainui's death meaning further details cannot be published at this stage.
The confirmation came shortly after Wainui's grieving wife Paige shared an emotional tribute on social media - receiving a tā moko in honour of her late husband.
Paige Wainui posted a video and photo on Instagram, her second post since her husband died.
"I don't have the words right now or could begin to describe the feeling of losing you baby all I know is I don't wish this on anyone," she wrote.
"I'm in absolute pieces and in so much pain knowing my whole other half to me has left this earth," she wrote in the caption.
"But I will forever celebrate you my love for being the most amazing and incredible husband & father you were and the special years we got to spend together on this earth."
The heartfelt message was accompanied with a video of Paige getting a tā moko - similar to that of Sean - on her ring finger by an artist who also tattooed Wainui.
"It was truly a special moment as he did Sean's mokowhiti to resemble our marriage and our tamariki."
Paige also thanked people for the "overwhelming support, generosity and aroha" they have shown her over the past week.
"The awhi has been out of this world. I am incredibly appreciative of you all thank you so much."
Wainui also leaves behind children Kawariki and Arahia.
He played 53 games for Taranaki before shifting to Bay of Plenty this year. He also played 44 games for the Chiefs, nine for the Crusaders and represented New Zealand Māori since 2015.
In June he scored five tries in a Super Rugby Transtasman victory over the Waratahs, the first player to ever do so in Super Rugby history.
Eulogies were given by a number of people at his tangi, including Wainui's siblings, father and the Taranaki coach.
"He was a star, he led the back three they called it 'bomb squad' so he could defuse those bombs. I was so proud of him, he took every ball and we were able to carry on and win the case because he inspired, he inspired us with his attributes on the field," a teary Colin Cooper said.
Wainui was spotted by coach Cooper and signed with Taranaki at just 18 in 2014.
Wainui's siblings Whitney and Luke Wainui also spoke.
"The four of us were extremely close and we held each other like the walls of a whare. You will be surely missed but always remain close to our hearts," Luke said.
Wainui's father Paul said his heart is starting to heal.
"I don't wish any parent to bury their own child especially this age, engari [but] God gives and God takes," he said.
A Givealittle page set up by the Chiefs to support the family has climbed above $269,000.
WHERE TO GET HELP:
If you are worried about your or someone else's mental health, the best place to get help is your GP or local mental health provider. However, if you or someone else is in danger or endangering others, call police immediately on 111.
OR IF YOU NEED TO TALK TO SOMEONE ELSE:
• LIFELINE: 0800 543 354 or 09 5222 999 within Auckland (available 24/7)
• SUICIDE CRISIS HELPLINE: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• YOUTHLINE: 0800 376 633 ,free text 234 or email talk@youthline.co.nz or online chat.
• NEED TO TALK? Free call or text 1737 (available 24/7)
• KIDSLINE: 0800 543 754 (available 24/7)
• WHATSUP: 0800 942 8787 (1pm to 11pm)
• DEPRESSION HELPLINE: 0800 111 757
• SAMARITANS – 0800 726 666.
