Dean Doherty came off his bike on Sunday at a dirt track in Magilligan. He was airlifted to the Royal Victoria Hospital in Belfast.
Doctors have told the family that he suffered serious spinal injuries.
His brother, Erol, said they are praying for a full recovery.
"He went in for surgery today (Monday) and they somehow secured his spine in place," he said.
"The doctors said he has a chance of walking, they said might walk, they didn't say for definite."
Erol said the family were remaining hopeful and that there were some good signs.
"The spinal cord is intact which is a good thing," he said.
"He has a little bit of feeling in his legs. We're hoping through physiotherapy that things will get better but the doctors reminded us that it's an uphill struggle."
Erol first became aware of the accident after a phone call from his mother.
"My mum was ringing me up and crying and saying he had been in some kind of motorbike accident," said Erol
"It was on his scrambler at a circuit he was on, the bike had somehow left him and, whatever way it had fallen, he had fallen on his pelvis and that had pushed up into the back of his spine.
"It just goes to show you the danger of bikes."
The family have said they are receiving lots of messages of support and said they were grateful for all the well wishes and prayers.
The family of a 26-year-old man from Limavady, County Londonderry, fear he might never walk again after an accident involving a scrambler motorbike.