The Daily Telegraph reported Rugby Australia and Folau settled the former Wallaby's wrongful termination claim for the large sum after the fullback initially sought $14 million in compensation.
However, Castle has come forward on social media to deny the report.
"Folau settlement numbers are confidential but numbers being speculated are wildly inaccurate," Castle said in the short statement.
Folau sought compensation from Rugby Australia after he believed he had his contract torn up wrongfully for a code of conduct breach on social media.
Folau's breach stemmed from an Instagram post earlier this year in which he said "Hell awaits" groups of people, including homosexuals and drunks.
Folau and Rugby Australia engaged in mediation this week and after a 12-hour meeting on Monday and follow-up lengthy phone calls after, the two parties announced yesterday they had reached an agreement after settling for a confidential amount.
The reported $8 million is much higher than many pundits expected with former Wallaby and Australian media personality Peter FitzSimons saying in a recent Sydney Morning Herald column he expected nothing higher than "$200,000 to $300,000".