Dad-of-two's horrific injuries after savage attack by pitbull
Mr Donegan, who is recovering in Beaumont hospital, was walking near Cromcastle Court in Coolock at around 8.30pm.
He noticed two other men walking a pitbull and became concerned for his own dog.
He asked the men to stay back with their more volatile animal.
However the pitbull then attacked, leaving him with severe scars and bite marks.
Mr Donegan was bitten a number of times and he suffered numerous bite injuries to his hands, leg and face.
In the course of the incident, his mobile phone was smashed as he fell to the ground.
"We are all very worried about Nicholas," said another of Mr Donegan's sisters, Maura Hancock.
"Dangerous dogs like that should not be allowed out in the open," she added.
The dad-of-two was rushed to the nearby Beaumont Hospital after a passer-by in a van came to his aid.
He was dropped at the hospital's accident and emergency department where he received extensive treatment.
Medics fear that "long term tissue damage" has been caused to the unfortunate victim.
It is understood that gardai from Ballymun Garda Station were then alerted to the vicious attack. A short time after he was admitted to the hospital, a man in his early 30's was arrested close to the scene while gardai seized the dog. The animal was put down the following day.
The dog's owner – who is from the Coolock area – was questioned at Ballymun Garda Station.