The darts player, known as Phil ‘The Power’ Taylor, met Jackson, who suffers with cerebral palsy, and his family at an event in Goven at the weekend.
The family, from Irvine, is aiming to raise £70,000 to send the youngster to America for treatment.
It was a chance meeting, but Taylor has pledged to get friends Robbie Williams and Ronnie O’Sullivan to boost the fundraising campaign.
Taylor had been playing Scot Gary Anderson at an exhibition at Fairfield Social Club when he met Jackson and his family.
He said: “I was introduced to him and I couldn’t help but want to do something. We got chatting and his family are also lovely and it’s just heartbreaking what he is going through and needs that treatment.
“The family were trying their hardest to raise the cash, but I can help immediately with the £20,000.
“I’m going to spend the next few days ringing round a few pals like Robbie and Ronnie and we’ll get the full £70,000 he needs.
“I was blown away by Jackson, I was almost in tears from the moment I met him. He’s such a lovely kid.”
The event was organised by Wullie Burns, who said: “Jackson’s grandfather plays darts in a team local to me in Irvine and asked me if they could come along to the exhibition with Phil and Gary to try and raise more money.
“We managed to get £650 and I was really pleased with that, but Phil just left us all gobsmacked by his generosity.
“I’ve not doubt that Phil will help them raise the £70,000 needed and that’s just incredible. I’m just so delighted because they’re a lovely family.”