Players' representative Todd Martin has undermined Greg Rusedski's claims that his fellow professionals will support him over his failed drug test.
Rusedski could find himself without too many supporters
Rusedski could be banned for two years after testing positive for nandrolone.
ATP Players' Council boss Martin said he would be comfortable with such a verdict, believing "the onus is on us to monitor what goes into our bodies".
But Martin added that Rusedski's test did not show "performance-enhancing levels" of the banned steroid.
Martin's comments are at odds with Rusedski's belief that he has the full backing of the players.
But Martin conceded that intent was a contentious issue, even though Rusedski's test sample showed illegal levels of nandrolone.
He said: "It is important to remember that the tests last year and this year are not to performance-enhancing levels."
Rusedski is using the argument that players have unwittingly taken banned substances contained in electrolyte drinks used to combat fatigue after long matches in intense heat.
In several cases, failed drugs tests have been linked to drinks given out by ATP trainers.
Martin admits "we've got these substances that appear perfectly legal", but he believes the only way to be certain of staying clean is to not take supplements.
It is a warning that Martin feels is not being heeded by the players
He said: "I don't think the players have heard it as clear as they need to. Unfortunately the message has to come in dramatic ways."