While the head of ASADA has said that only the laboratories in Cologne, Germany, and Montreal, Canada, have the capability of testing for performance-enhancing peptides, the AFL is understood to have been advised that the samples from players may well disintegrate over the journey.

Experts have suggested to the AFL that the substances in question - thought to be peptides that release human growth hormone within the body - might not be sufficiently preserved in Cologne or Montreal. But the decision on whether to send Essendon samples overseas would be made by ASADA, which controls the testing, rather than the AFL.

If the samples cannot be sent overseas, then the AFL and ASADA would almost be entirely reliant on detective work - and the evidence of players - in determining whether Essendon has taken any performance-enhancing substances.

Essendon has maintained that its players took only vitamins as far as it knows and has been increasingly confident about its prospects of being cleared in the investigation. The club's players have not yet been interviewed by ASADA or the AFL, and will play in the NAB Cup on Friday evening.

The limitations of testing in investigating potential performance-enhancing drugs has been a massive issue for sport internationally, and the most spectacular successes in detecting cheating - the Lance Armstrong case, and the BALCO case involving Marion Jones - have all been on the back of detective work and testimonies of people involved, rather than testing.

The former head of ASADA, Richard Ings, said that sending samples overseas for testing had been standard practice when he ran ASADA, but that the test for peptides was ''brand new'' and this might explain complications. The samples also would be being tested for a second time, he said.

''It's a very, very standard thing to do … this is a brand new test. There may be something special about it, that is different to ones I used before. I wouldn't be doubting the AFL - I mean, if there's a chance to get them tested and get it done, they would do it. Also, it would be ASADA that would be making that decision, it would not be the AFL.''

Sports doctor Peter Brukner wrote in The Sunday Age on the weekend that the HGH ''precursors'' that are central to the question of whether Essendon breached the drug codes were, ''in effect … undetectable.''

Brukner said that athletes had turned to these precursors, or peptides that release HGH in the body, because ''they are extremely difficult to detect''.

''Instead of taking the banned and possible detectable HGH, those intent on improving performance have turned to the growth hormone precursors as an alternative,'' he said. ''There is no evidence that these substances work, but certainly there is a theoretical rationale behind their use.''