Zac, from Broseley, who has a rare form of leukaemia, has been unable to get the treatment he needs on the NHS, but thousands of people across Shropshire and beyond have come together to fund his £500,000 trip to America.
However, due to an infection he is unable to travel abroad until he recovers.
His father Mark Garbett said he will travel to a children's hospital, in Philadelphia, as soon as practicable.
"We would have liked to have been there last week but unfortunately Zac came down with an infection and it really set him back.
"Unless he's healthy he can't fly because it's such a long flight, but his immune system is boosting and up he's doing well. I think we would anticipate to be there next week," Mr Garbett said.
Zac's family have confirmed that the money needed to pay for his treatment had cleared from the JustGiving page that was set up for the successful online appeal and that they had been able to transfer the money needed to the hospital.
They have also received visas to travel.
How you can help:
- Anyone who wants to support the fundraising campaign should visit justgiving.com/crowdfunding/zac-oliver
- People can also join Zac's Facebook support page which is called 'Zachariah's's fight against Acute Lymphoblastic Leukaemia'.
- People can also donate using their mobile phone by texting ZACH75 £1 to 70070.
Zac has an extremely rare form of childhood leukaemia called Near Haploid, and the specialist treatment required is unavailable on the NHS.
Donors from across the world including a number of celebrities helped to raise the mammoth total needed to get him to America, where he will be able to receive the specialist CAR-T therapy.
Fundraising activities have included a mysterious £100,000 donation, a 24-hour sponsored football match organised by Broseley Youth Sports, a Wear Red for Zac Day, Telford Town Park ZacFest, collections, raffles, a lorry convoy, and the youngster was guest of honour at AFC Telford United.
Among the groups putting their shoulder the wheel to assist the appeal was the Side by Side Ukes ukulele band held a busking event in Wellington.
Last month he was also treated to a day out to watch Wolverhampton Wanderers play Watford, and Shropshire Council has named a snow gritting vehicle after him in a show of support.
Although the initial online £500,000 target has been reached family and friends are continuing to fund raise to cover other medical expenses and eight return trips to the US for follow up appointments, accommodation for each bone marrow biopsy, day/night feeds, and out-patient medication.
Any additional funds not needed will be specifically used for research into childhood cancer or used to provide treatment for other children in a similar situation to the youngster.