Mo Farah's coach Alberto Salazar is alleged to have regularly carried a banned steroid gel with him to training camps.
Accusations have been made by Allan Kupczak, who worked as a massage therapist at the Nike Oregon Project from 2008 to 2011.
Earlier this month, BBC documentary Panorama uncovered allegations of doping offences involving Salazar and American long-distance runner Galen Rupp.
Now, Kupczak has told The Guardian that the 56-year-old would regularly take Androgel to training camps and would warn athletes not to touch his bag in fear of them being contaminated with the testosterone substance.
Kupczak told the newspaper: "When we were at an airport together Alberto would say, 'don't let anyone touch my bag. I have my testosterone cream in there. I don't want anyone to get contaminated accidentally.' My thought was, if you are taking testosterone for yourself there are so many ways you can do it.
"You can do it in a tablet form. You can do it injection form. You can do it in an implant. So why risk something that could possibly contaminate the athlete? That is nuts. But then we would say, it's his way - that's Alberto."
Salazar, who is also alleged to have once had a bag of needles at a training camp, has strongly denied all doping allegations.
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