London - Leading American coach Alberto Salazar has encouraged athletes in his care to take banned substances, a documentary screened by the BBC on Wednesday claims.
Salazar, 56, who coaches Britain's two-time Olympic champion Mo Farah, is alleged to have doped Olympic silver medallist Galen Rupp, the USA's national 10 000m record-holder, in 2002.
Both Salazar, an athletics great who won three successive New York marathons, and Rupp deny any wrongdoing, while there is no suggestion that Farah has broken doping rules.
The investigation by the Panorama programme centres on the Nike running camp in Portland, Oregon, where Salazar is the head coach.
Steve Magness, who worked as an assistant to Salazar at the Oregon Project in 2011, said he saw a document showing Rupp's drug levels, which revealed the then-teenager was taking prohibited testosterone medication.
"When I saw that, I kind of jumped backwards," Magness, a former athlete, tells the documentary.
"Testosterone is obviously banned... Everybody knew that. When I looked a little further, I saw it was all the way back in high school, and that was incredibly shocking."
The documentary also features testimony from athletes and staff who worked with Salazar at the Oregon Project and who accuse him of facilitating the use of banned substances and illegal practices.
In a statement to the BBC, Salazar said the "allegations your sources are making are based upon false assumptions and half-truths in an attempt to further their personal agendas".
Salazar says the 'testosterone medication' on the document seen by Magness was an erroneous reference to the legal nutritional supplement Testoboost.
Rupp, 29, strongly denies the allegations in the documentary, saying: "I am completely against the use of performance-enhancing drugs."
Farah, who won gold in the 5 000m and 10 000m at the London 2012 Olympics, told the BBC: "I have not taken any banned substances and Alberto has never suggested that I take a banned substance."
Farah, 32, has worked with Salazar since 2011. Rupp, who took silver behind his training partner Farah in the 10 000m at the 2012 Olympics, has been a member of Salazar's stable for 14 years.
None of the Nike Oregon Project's athletes has ever failed a drug test.
Annie Skinner, spokesperson for the US Anti-Doping Agency said the agency "aggressively follow up" reports of doping.
"With that said, we do not confirm or deny the existence of any investigations ... we follow the evidence and in circumstances where the process results in credible evidence of doping we bring cases through the applicable legal process," she said.
"It is important to re-emphasize USADA's position that all athletes are innocent until and unless proven otherwise through the established legal process. Attempts to sensationalize or exploit either the process or the athletes are a disservice to fair play, due process, and to those who love clean sport."
However, David Howman, chief executive of the World Anti-doping Agency (WADA), said he believed the documentary's claims warranted scrutiny.
"I would be not only disturbed, I would be very disappointed and that's why I think it needs to be scrutinised by us as an independent body," he said.