Nicholas Tadros, 10, was on board one of two helicopters involved in the crash at Sea World on January 2.
His mother Vanessa Tadros, British couple Ron and Diane Hughes, and pilot Ashley Jenkinson died after the two aircraft collided mid-air and one crashed into a sand bar.
Family friend Charlie Bakhos said the grade 5 student had suffered a "significant setback" and might need to have his right foot amputated after a surgical operation could not be completed.
"(His father Simon) will have to face Nicholas in the coming days to let him know his mum been taken to heaven and also let him know that he may be losing a foot, which will be a major blow to (Nicholas's) mental state of mind," Mr Bakhos wrote in a Facebook post on Saturday.
The Bethany Catholic Primary School student remains in a critical but stable condition in Queensland Children's Hospital after waking from a coma last week.
The news came days after hundreds of mourners paid tribute to his mother at a funeral service at Saint John the Beloved at Mount Druitt, in Sydney's west.
An online fundraiser for the family had raised more than $63,000 as of Saturday afternoon.
The results of a probe into the collision by the Air Transport Safety Bureau are not expected until at least September 2024.
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