A transplant was the youngster's only option to survive – and his family faced a desperate race against time to find a donor match before the illness caused irreversible damage to his organs.
Fortunately James Evans came to the rescue by donating his bone marrow despite not knowing who the recipient would be.
O'Neill is still planning without Seamus Coleman and Jon Walters with no expectation they will defy medical predictions and come back in time.
Shane Duffy was the leading Irish performer in a stirring defensive display in Cardiff and O'Neill is hopeful that the Brighton player will be back after sustaining a groin injury against Everton on Sunday.
The touching video, created by the Welsh Blood Service, captures the first meeting between the little boy and his saviour.
Mother Nadine Pullen, 27, is seen asking Jack 'What did James do?
And while the boy was placed on the waiting list, James, 26, a researcher in the Cardiff Medicentre at the University Hospital of Wales, came forward to donate his bone marrow on December 18, 2014.
The family, who live in Portsmouth, were overjoyed to find out there had been a match and Jack received the transplant the very next day at Great Ormond Street Hospital in London.Without the enzyme, sugar can build up and damage vital organs such as the heart.Hurler syndrome is progressive, and incurable, but a blood or bone marrow transplant can stave off the ravaging effects.At the time Nadine said: 'I wouldn't have the little boy I know and love today if it wasn't for this man.' So she made it her mission to personally thank the big-hearted man responsible for saving Jack and launched an appeal on social media.Wales Online ran a story about it, and James was found.Ireland's manager was also keen to play the second leg in Dublin and that wish came to pass with the first leg in Copenhagen on Saturday, November 11 before the decider takes place at the Aviva three days later on Tuesday, November 14.