The Daily Telegraph claims the 25-year-old underwent a drug test after a match this season against Melbourne Heart and it revealed traces of a recreational drug.
The newspaper added that the former Olyroo, who has made 30 appearances for the Mariners since 2011, fronted a tribunal a fortnight ago after his contract was terminated two months ago.
In a media release titled 'Clarification regarding Troy Hearfield' however, the club wrote: "Central Coast Mariners wish to advise that Troy Hearfield approached the Club in early February seeking a release from his contract. The Club and Troy then mutually agreed to terminate his contract at that time.
"No further comment regarding this matter will be made by the Central Coast Mariners until such time as the process is complete."
Before joining the Mariners, Hearfield racked up 66 games over three seasons with Wellington Phoenix after a stint with Newcastle Jets.