The sports scientist at the centre of the Essendon drug scandal, Stephen Dank, used an unfounded allegation about Collingwood using banned drugs to pressure coach James Hird to authorise the controversial peptide program, according to a key witness in the investigation.

Biochemist Shane Charter, who has spoken to ASADA several times including in the past week, has explained that Dank asked him to verify that the Magpies had been using human growth hormone in order to persuade Hird to get the peptide program ''over the line''.

Charter, who sourced the peptides from China, said he flew to Queensland at Dank's request in December 2011 to help sell the program to Hird. He said he had never sold or supplied Collingwood with substances or had knowledge of their supplement program.

''Dank had been telling Hird that Collingwood was on human growth hormone and that we had to get the peptide program over the line,'' Charter said in a previous interview with Fairfax Media. It is understood Charter has given the same information to ASADA, which will hand down its report on Essendon in coming days.

''He said to James when I was there, 'Shane will prove my point.' He was talking about HGH,'' Charter said. ''He was saying that, 'Shane has his ear to the ground on who is using it.'

''I had no knowledge. I didn't sell, supply or know anything about the Collingwood program.''

Charter said Dank had ordered the peptides months earlier in 2011 and was ''determined to make sure the program went ahead''.

Collingwood president Eddie McGuire, who is travelling in the US with AFL chief Andrew Demetriou as part of an AFL delegation, used his Triple M radio program on Thursday morning to say that Hird had been in contact with him and that the Essendon coach had denied he ever suggested to former conditioning boss Dean Robinson that the Pies were taking HGH.

On Wednesday night, Robinson told interviewer Luke Darcy on the Seven program that Hird had allegedly said of Collingwood:

''He [Hird] wanted me to bring bigger and stronger players to him. He felt they were being out-muscled, and he specifically noted a side that he really wanted to be. He wanted to go after Collingwood, and he wanted to be Collingwood. And he knew the stuff that Collingwood were doing. He said to me that he knew that they were taking supplements, that were allowing them to get an advantage, because he knew who was supplying them.''

The Pies also issued a statement calling the suggestions of undetectable performance-enhancing drug use were ''totally false''.

Robinson's comments followed the reporting of text messages between Dank and Hird that have dragged the Magpies, Hawthorn and West Coast into the Essendon quagmire, with those clubs angrily denying the suggestions in Dank's texts that they were ''biologically advanced''.

Charter has told Fairfax Media that he has co-operated fully with the ASADA investigation and answered questions about his relationships with Hird, Dank and the compound pharmacist Nima Alavi, who provided supplements to Dank. Charter has handed over a series of text messages and emails to the investigators, including those that establish his commercial relationship with Dank.

Charter, a former bodybuilder, has also said he stopped providing Dank with peptides in late April last year because Dank had missed payment deadlines.