Rio Ferdinand's eight-month suspension for missing a drugs test has been labelled both harsh and lenient.
Dick Pound, chairman of the World Anti-Doping Agency, believes Ferdinand "did very well to get only a third of the penalty which he may be liable".
Pound was referring to the two-year ban which applies to athletes in other sports who fail to take a drugs test.
But Professional Footballers' Association chief executive Gordon Taylor, said the ban was "draconian".
An independent tribunal found the Manchester United defender guilty of misconduct after he failed to take a test on 23 September.
The ban, which provisionally starts from 12 January, would see him miss the rest of the season and Euro 2004.
BANS IN ENGLISH FOOTBALL
Nine months and community service for kicking a fan
Nine months after failing a
drugs test for cocaine
Eight months and £50,000 fine for failing
to take a drugs test
Six months (suspended for three years) and £20,000 fine for commentary in a video glorifying football violence and dirty tricks
Five weeks, and £150,000 fine for
comments made about Alfie Haaland in his autobiography
United have already indicated they will appeal against the punishment.
But Wada chief Pound issued a warning over their intention to contest the decision.
He told the BBC: "I think Rio should be careful over an appeal against sentence - as it could be increased.
"I don't know what the disciplinary board heard that caused them to give a penalty that is only a third of the maximum.
"They have obviously heard something they feel mitigates the penalty.
"But it is clear they have rejected any suggestion that Ferdinand accidentally failed to take the test."
Pound added that he was surprised Ferdinand's ban would not take effect immediately, leaving him available to play until 12 January.
"If guilt has been determined, it is clear there will be some kind of sanction. I don't understand why he, his club, the FA or Fifa would want him to play," he said.
By contrast, PFA chief executive Gordon Taylor, who has supported Ferdinand throughout, told BBC Radio Five Live: "We knew there would have to be a penalty. But an eight-month ban and £50,000 fine is, I feel, very draconian."
"I felt there was every opportunity for the FA to give him the benefit of the doubt."
John Scott, the man currently in charge of doping issues at testing agency UK
Sport, backed the FA's handling of the matter.
He explained: "It's the responsibility of the FA to set the
penalty - and while the recommended ban for this sort of offence is two years,
they have obviously taken account of the circumstances.
"Our main concern with any doping offence is that the governing body follows
the rules and regulations, and we are very satisfied that the FA has gone
through a proper process and a proper hearing."
But former England manager Graham Taylor believes there are many lessons for football as a whole to learn from the Ferdinand furore.
"Everybody in football has to understand how important it is that we are drug
free," he told BBC Radio 5 Live.
"The message to all professional footballers is 'You do not forget if you are
being asked to take a drugs test'.
"The clubs and managers have to make it abundantly clear to young
professional footballers who are earning tremendous amounts of money that they
do not succumb to temptations.
"Professional football must understand it has to take responsibility for this