The FEI confirmed a sample taken from Walker on August 7 tested positive for benzoylecgonine, a metabolite of cocaine.

The sample was taken on the day of the test showjumping final at the Pan American Games in Lima, where the Canadian team finished fourth.

Canada secured a Tokyo 2020 quota place due to their finishing position, with berths awarded to the top-three teams who had yet to qualify for next year's Games.

Brazil, Mexico and Canada would receive the places.

The FEI say that under Panam Sports Anti-Doping rules, an anti-doping violation by a member of a team, outside team sports, also leads to disqualification of the result obtained by the team in that competition.

This could lead to Canada losing their Tokyo 2020 berth, should Walker prove unsuccessful in appealing the decision.

Walker has requested a preliminary hearing before the FEI Tribunal to apply for the lifting of the provisional suspension, as well as a hearing before the Panam Sports Disciplinary Commission.

The FEI say they will be in a position to make any necessary reallocation of the Olympic quota place, once the Panam Sports Disciplinary Commission made a final decision on the potential disqualification of Walker and Canada's team place.

Walker has denied using banned substances.

"I do not use illicit drugs, ever," she said, according to Horse and Hound.

"Whether in Peru, or in any competition setting for that matter, I am always fully aware of the possibility of being tested and would never expose myself to any substance that could test positive.

"My Canadian team mates, my team in the barn, our horses and I, have all put a lifetime of effort towards an Olympic goal and I would never do anything to jeopardise that for my team mates or for myself.

"I'm extremely grateful to everyone for their support and to my team mates for standing with me."

Equestrian Canada have given Walker their support, following confirmation of the suspension.

"Equestrian Canada is firmly committed to clean sport," a statement read.

"We also believe in standing behind our athletes, and fully support Nicole during this challenging situation.

"Equestrian Canada will be working closely with Nicole and her legal team as appropriate next steps are determined."

Canada are one of 20 teams currently qualified for the team showjumping competition at Tokyo 2020.

Hosts Japan will feature with the United States, Sweden, Germany, Switzerland, the Netherlands, Australia, Belgium, Britain, France, Israel, Ukraine, Brazil and Mexico.

Egypt, Qatar, New Zealand, China and Ireland are also among the qualifiers.

Argentina placed fifth behind Canada at the Pan American Games and could potentially benefit should they be disqualified from the competition.