The mother of banned footballer Jarrod Mullen says her son is in a state of despair after being "hung out to dry" by the Newcastle Knights and the NRL.

In May, the NRL banned Mullen for four years after he earlier tested positive to a banned steroid, which he claims he unknowingly received as part of a physiotherapy treatment.

His mother, Leeann Mullen, said the way her son had been treated was inconsistent with the "second chance" approach afforded to other players.

"He's certainly been hung out to dry, I believe," she told ABC News.

"He's been denying that there's anything wrong for a long time, he's putting up a brave front.

"We've all crumbled around him and he's been the really brave one."

Jarrod Mullen and his mother Leeann Mullen at Newcastle Knights function before his suspension. ( Supplied: Facebook )

The Australia Sports Anti-Doping Authority (ASADA) in March recommended Mullen be banned for four years, however he chose not to accept the punishment and appealed to the NRL anti-doping tribunal.

Mullen delivered a positive result for Drostanolone after a routine swab test during preseason training last year.

He played 211 matches for the Knights following his 2005 debut, and made one State of Origin appearances for the Blues.

However, the ban effectively ended the 30-year-old's career.

Mullen has always claimed he had no knowledge he had been given a banned substance and did not consent to it.

Punishment was too harsh, says mum

Ms Mullen said her son's penalty was too harsh, and that she had written to NRL chief Todd Greenberg to complain about the punishment.

"There's lots of other incidents in the NRL, in recent history with players around recreation drugs," she said.

"There's been match-fixing allegations, there's been the Cronulla drugs saga.

"There's been domestic violence, there's been a whole range of off field issues that NRL players have been embroiled in.

"I believe most of them have gotten off pretty lightly."

Despite his initial bravery, Ms Mullen said her son was now struggling to come to terms with his suspension.

"He's tried to be really brave for all of us," she said.

"But I think that's taken it's toll after six months, of him pretending there's nothing wrong."

In a statement, the Newcastle Knights said they had handled the issue "directly with Jarrod".

"The club understands this is an emotional time for Jarrod and his family, given Jarrod's significant contribution to the club," a spokesperson said.

"The club has offered support to Jarrod and his family throughout this difficult time and remain as disappointed as his family in regard to the premature end of his career at the club."

Ms Mullen claimed Knights players had been told not to associate with her son, but Newcastle coach Nathan Brown rebuked that statement.

"We all went for lunch at his restaurant about three or four weeks after it happened, and Jarrod was there, so where they can't associate with Jarrod is at training and that's because of ASADA," Brown said.

"That's not because of the Knights, or Nathan Brown, that's because of something that Jarrod's done, not something the Knights did."