“I can’t thank him enough. Wow. I wasn’t expecting that.
“I sent Louis a text personally saying thank you. All the boys from One Direction mean the world to me.
“I met up with all the lads again at Liam’s funeral exactly a year ago.
“It was the saddest time ever but a lovely reunion.”
Mahon’s friend Tracy Trigg set up a GoFundMe page to save her pal’s legs.
After Tomlinson’s donation, more donations have flooded in and the total passed £11,000 on Saturday.
Mahon said he “desperately” needs a second operation to avoid having to live the rest of his life with pain.
“My dad organised for me to see an expert in Madrid who did his knees,” he said.
“He phoned my father after the op and told him, ‘We just did life-saving surgery on your son’.
“After the operation, it felt like a weight had been lifted off my shoulders but now I desperately need this second operation to have a chance of living out my years without pain.”
Mahon said he is only asking for donations because he has “nothing left” in the bank.
“I’ve never asked for money but I’ve got nothing left.
“My family finances have been exhausted.”