Leeds Rhinos legend Rob Burrow has been diagnosed with motor neurone disease (MND).
He won eight Grand Finals, three World Club Challenges and two Challenge Cups in 17 years with the Super League side.
Burrow, 37, who also won 15 caps for England, retired in 2017 and is now the club's reserve team head coach.
"It was a bit of a shock. I'd not had any sort of prep for being told that you have something where there's no cure," he told BBC Look North.
"It's one of the frustrations, the doctors and specialists don't know how you got it, and there's not much they can do.
"You don't know much about your life expectancy, for example Stephen Hawking lived 54 years with it.
"Maybe it's the athlete in us all, we don't want to lie down and just take it, we want to compete.
"I'm going to get stuck into it, a bit like my career I was doubted and written off a few times so I'm really positive, taking the challenge and that's the best way to be.
"It was a numbing moment, but a week further on [from the diagnosis] I'm in a decent place."
MND is a degenerative condition that affects how nerves in the brain and spinal cord function, and as Burrow confirmed there is currently no cure.
Rhinos director of rugby Kevin Sinfield, who played alongside Burrow for both Leeds and England, said the news was "devastating and heart-breaking".
Sinfield added that Scotland rugby union great Doddie Weir, who revealed in June 2017 that he had been diagnosed with MND, has met with Burrow.
Weir was honoured with the Helen Rollason Award, which recognises outstanding achievement in the face of adversity, at the BBC Sports Personality of the Year event on Sunday.
The former British and Irish Lion has set up a foundation, which Burrow is keen to support going forward.
"I really want to get involved in Doddie's work, trying to find something for MND," he added.
"I've total family support, my club and in particular Kev [Sinfield] can't do enough for me so I'm really lucky, while Doddie's got help from his rugby (union) background.
"The man or woman on the street who gets told, like the postman as Doddie says, has no help or funding so to raise money for them as well as yourself is really important."
Leeds have announced that the testimonial for Jamie Jones-Buchanan against Bradford Bulls on Sunday, 12 January at Headingley will now be a joint-fundraiser for Burrow as well.
Former England captain Sinfield said: "Throughout his career, Rob overcame the odds to become a legend of the game and I know he will tackle this challenge with the exact same positive determination.
"As a club, Rob will receive our full support and we will be working with him to chart the way forward."