Japan's Olympic chief has slammed a top canoeist for spiking a rival's drink with a banned substance to scuttle his Tokyo 2020 selection hopes, describing his act as "unthinkable".

The Japan Anti-doping Agency last week banned Yasuhiro Suzuki for eight years for putting a prohibited muscle-boosting agent into the drink bottle of fellow sprint canoeist Seiji Komatsu during a domestic competition last September.

Canoe officials branded Suzuki's actions "evil" and Japan Olympic Committee (JOC) president Tsunekazu Takeda also blasted the disgraced athlete Friday, accusing him of bringing shame on Japan before next month's Winter Olympics in Pyeongchang.

"For a scandal like this to break as we head to Pyeongchang is extremely sad," Takeda told AFP.

"It was an unthinkable act and totally goes against the spirit of the Olympics. It's a real shame and we cannot afford to let this kind of thing happen ever again."

Suzuki admitted to spiking the drink after receiving an intensive anti-doping lecture during a training camp, according to the federation.

"We meet top athletes regularly to teach them the importance of maintaining their credibility and still this has happened," said Takeda.

"I met with all the Olympic organisations yesterday and called for them to go back to the drawing board and make sure this doesn't happen again."

The Japan Canoe Federation could still impose a life ban on Suzuki, 32, citing a history of sabotaging rivals, sometimes by stealing their equipment.

Komatsu won the race in September but was later provisionally suspended after he tested positive for the drug, which he strenuously denied using. His suspension has now been lifted.

Both Suzuki and Komatsu were among the top candidates to represent Japan at the forthcoming 2020 Olympics.