JOBE Watson and Dustin Fletcher could be disadvantaged in any anti-doping penalty because they played in the international rules series against Ireland, the Players' Association has conceded.

The AFL Commission gave the pair permission to play for Australia in November last year.

With a decision from the AFL Anti-Doping Tribunal expected by the end of March, all Essendon players still with the club from 2012 will sit out the upcoming NAB Challenge so they don't jeopardise the backdating of any suspension.

But AFLPA chief executive Paul Marsh has admitted the interruption to the Watson and Fletcher provisional bans will have an impact.

"I think you have to go back to when that actually happened, and that was right around the time that provisional suspensions were put in place," Marsh told 3AW. 

"Those two particular players had their provisional suspensions start a week later and that will impact until the end of this," he said.

"(If the) players are found guilty, that one extra week will be a factor for those two. But one week versus the four- or five-month credit they have built up, is two significantly different things."

The 34 past and former Bombers players charged with using banned peptide Thymosin beta-4 have been provisionally suspended since infraction notices were issued.

ASADA confirmed on Wednesday that anyone who played during his provisional suspension would have any potential backdating of a suspension affected if he was found guilty.

"Our view is any athlete competing during their provisional suspension and prior to a final decision by a sport tribunal has not respected their obligation under the World Anti-Doping Code and should not be entitled to a credit for the provisional suspension," an ASADA spokesperson said in a statement provided to

Marsh also revealed the contingency planning was underway to allow Essendon to top up its list for longer than the NAB Challenge period should "the worst happen" and a large number of players are suspended for the season proper.

"We're absolutely talking about that, we have to, it's only six or so weeks away," Marsh said.

"As you can imagine, it's complex.

"We've got through issues like how we're going to pay the top-up players, what insurance will be in place, what happens if they have to quit jobs to come and play in the competition, how will the salary cap be impacted.

"There's a lot of work going into it, and hopefully it'll all be wasted work in that the players will be exonerated here.

"You can't wait until the verdict's handed down here and then start thinking about it.

"I'm confident if the worst happens that we'll have answers as to what we do next."

Essendon is likely to require top-up players for at least the NAB Challenge, with its first game against St Kilda in Morwell on Saturday March 7.