It is alleged Gallen said to a young fan who was waiting for autographs after a game three weeks ago: "F**k this, I haven' got time for this sh*t."
Gallen has angrily rejected the claims and called on the Sharks to conduct an investigation into the alleged incident he claims never happened.
But the father, who doesn’t want to reveal his name publicly, is sticking to his story.
"I heard (Gallen) crystal clear," he told the Daily Telegraph.
"And then he has flicked the magazine back at my son and walked off and Flanagan was maybe five metres behind him.
"And as Gallen was walking off, I was going, 'Are you serious? Did this just happen?'
"And that is when (Flanagan) came straight over and apologised.
"I was disgusted. That is why we thought we would send a letter to the club and see how they reacted.
"And to be honest, by their comment saying they would 'deal with it internally but we have your best interests at heart', that is the old sweep-it-under-the-carpet line.
But Flanagan has a different recollection of the alleged incident.
"To say I witnessed it is incorrect," he told the Daily Telegraph.
"I was probably 20 or 50 metres away. I didn’t hear anything. I just addressed it the best way I could.
"The bloke was disappointed and I said I will get the stuff signed. He didn't tell me there was an issue at the time."
But the father remains adamant and demanded an admission from Gallen.
"I know what went on and the boys witnessed it all," he said.
"I have nothing to hide and nothing I said is what didn't happen.
"We don't want anything out of this, just for him to be man enough to admit it."