The 31-year-old said that after being left out of the derby match against Hull FC, he knew his time at the club was coming to an end.
Mason said: “It was gut-wrenching being left out for the derby as that was all that people had talked about since I signed.”
The former Australian international, previously hailed as Hull KR’s biggest ever signing, joined French rugby union side Toulon last month and was a surprise inclusion for the Barbarians squad that faced England last Sunday.
The New Zealand-born prop said: “I didn’t come over to be loaned around like some reject, no way. Anyone in their right mind would not hang around if they were put in the situation I was.”
After fighting off competition from Huddersfield to capture the former NRL star last September, Hull KR had hoped he would obtain a Tongan passport, the country of origin of his mother.
That would make him a non-overseas players according to Super League rules, and mean the Australian scrum-half Michael Dobson could regain his place on the overseas quota following his recovery from an ankle injury.
Mason failed to obtain the required passport, and was unable to gain entry to the country until March when he travelled to Tonga on a holiday visa.
He was then de-registered the day before the Hull derby to facilitate Dobson’s returned to the squad.
On his omittance from the match, Mason said: “That was probably the beginning of the end for me at the club.”
Hull KR reportedly stopped paying the prop’s wages after citing a breach of contract after he visited the rugby union side Toulon on a day off without permission.
He has since joined the French Top 14 side, despite not playing union since his school days.
It is the latest chapter in the tale of controversy that has been Mason’s career.
He was fined $25,000 by the Canterbury Bulldogs in 2003 for testing positive to an illicit social drug reported to be an amphetamine.
In 2007, he was involved in an altercation at a nightclub with rookie centre Richie Williams and voted the NRL’s most hated player for the third year in a row.
He was twice fined for urinating in public while playing for Sydney Roosters in 2008 and 2009.