The NRL's integrity unit is investigating a photo which shows Australia Test star Valentine Holmes posing with a bag of white powder.
The NRL and Holmes' club, North Queensland, confirmed they are aware of the photo.
"The North Queensland Cowboys are aware of a photo posted to social media by a Cowboys player this morning," the club said in a statement on Sunday.
"The club is conducting an investigation as well as assisting the NRL Integrity Unit.
"The Cowboys will make no further comment until the investigations are completed."
Holmes uploaded the photo to his own Instagram account before deleting it.
It is not known what the substance is and there is no implication of wrongdoing on Holmes' part.
Holmes represented Australia during last year's Rugby League World Cup and was also part of the Queensland State of Origin side which won the 2023 series.
The 28-year-old sat out the Cowboys' final four games of the season due to suspension as the club missed out on a place in the finals.