The 178-gamer represented the Brisbane Broncos (24 games), Gold Coast Titans (56 games) and South Sydney Rabbitohs (98 games), playing every game for the struggling Rabbitohs in 2025 as they battled a lengthy and deep injury crisis.
Arrow also represented Queensland 12 times between 2018 and 2023.
He had not taken to the field in 2026.
South Sydney had issued a concerning statement in March saying that Arrow had undergone "a series of investigations over the past four-to-six weeks on his shoulder", ruling him out for at least a further six weeks at the time.
The 30-year-old said in a club statement that he had been undergoing extensive testing throughout 2026 following the experience of various symptoms which "have affected different parts of (his) everyday life".
MND is an incurable and degenerative disease that impact neurons in the brain and the spinal cord, with the ability to move, speak, swallow and breathe being slowly and gradually shut down.
Arrow will continue to undergo further testing and medical procedures as he and his loved ones navigate the most difficult time of his life.
“On medical advice, I am not currently medically cleared to train or play at the required level, and I will be stepping away from those duties while I focus fully on my health, treatment, and rehabilitation," Arrow said.
“I want to sincerely thank everyone at the South Sydney Rabbitohs for the personal support they have shown me and my family throughout this process.
"The South Sydney Rabbitohs, my teammates, staff, and everyone behind the scenes have made an incredibly hard situation much easier to face.
“To my teammates, thank you for treating me exactly the same every single day. Within minutes of walking through the doors, most of you are still making me laugh with the usual banter, and honestly, I wouldn’t want it any other way.
“To my family and closest mates, thank you for standing beside me through all of this. I know the road ahead won’t be easy, but anyone who knows me knows I’m competitive, stubborn, and ready to fight this with everything I’ve got.
“What I need right now isn’t sympathy or sadness. What I need is support, understanding, and privacy while my family and I navigate this difficult time.
“This is only part of my story, and when the time is right, I’ll share more. But for now, I ask everyone to respect my privacy while I continue working with my doctors and my family.”