Media reports say 22-year-old Charanpreet Singh Lall registered "high levels" of cocaine in a random drugs test at his barracks. He was among the three who failed the test at Windsor's Victoria Barracks.
"Guardsman Lall has been discussing it openly in the barracks. The Guards carry out public duties at the Palace, it's disgraceful behaviour," a source was quoted as saying by the report published in The Sun.
"It is for his commanding officer to decide if he gets the boot but anyone caught taking Class A drugs can expect to be dismissed."
"Everyone's shocked. He was put in the limelight and now he's brought only embarrassment," the report said.
Lall’s family shifted from Punjab to UK when he was in infant. He was inducted into the British Army in Janruary 2016.
The beleaguered soldier facing ignominy grabbed world attention for being a part of the 1000-strong ceremony marking the Queen's 92nd birthday wearing a Sikh turban instead of a bearskin hat.
While Queen Elizabeth II celebrated her actual birthday on April 21, the Trooping of the Colour ceremony takes place on any Saturday of June. The ceremony has commemorated the birthday of the sovereign for more than 250 years and also functions as a display of army drills, music and horsemanship, according to news agency PTI.