"It doesn't make any sense to me, people taking drugs to play tennis," the Swiss said on Wednesday.

"We all would like to see our sport remain clean. But there are reports of several substances being used by players. Some of them may be energy supplements, but being professionals, the players should know what to use and what not to use.

"It's hard to believe some of them saying that they didn't know what the substance was."

Koubek, the world number 60, claims he was given the banned substance triamcinolon acetonid in an injection administered by an Austrian doctor for a wrist injury, despite being assured by the doctor that the injection contained no illegal substances. He plans to appeal to against a three-month suspension.

Earlier this year Briton Greg Rusedski escaped punishment after testing positive for nandrolone by arguing successfully that contaminated supplements provided by the men's ATP Tour were responsible.