Dr Richard Freeman's legal team will attempt to question the "integrity and credibility" of former British Cycling performance director Shane Sutton at a medical tribunal in Manchester.
Dr Freeman admitted a string of charges at a hearing at the Medical Practitioners Tribunal Service (MPTS) to determine his fitness to practise medicine.
They include ordering testosterone to British Cycling headquarters in 2011, lying to a UK Anti-Doping investigation and attempting to cover up the delivery.
Freeman, employed as a doctor by British Cycling and Team Sky for six years, says 30 sachets of Testogel were for Sutton, who has denied that claim.
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Freeman's lawyer Mary O'Rourke QC said her team were "gathering information on Sutton that questions his integrity and credibility" after being contacted by "individuals".
"We are duty-bound to check them," she added.
She also said she was attempting to contact former Department of Culture, Media and Sport chairman Damien Collins, who published a doping in sport report in 2018 which found that Team Sky and 2012 Tour de France winner Sir Bradley Wiggins "crossed an ethical line".
O'Rourke said she has "reasons to believe Collins was given a quantity of information that did not get published in its report, related to Sutton".
Later on Thursday Collins responded to correspondence from Freeman's lawyers, saying that materials that had not been reported in parliament could not be released, adding that all submissions were carefully considered.
O'Rourke said allegations of bullying will also form part of Freeman's defence and indicated that she would make an application to a newspaper to see what information they held in relation to the case.
At the hearing Freeman admitted to 18 of 22 charges, nodding his head as they were read out as the tribunal started.
The four he contests surround whether he ordered the testosterone, which is banned under the World Anti-Doping Code, for an athlete to improve their athletic performance or whether he "knew or believed" that was the case.
O'Rourke said they would call on former British Cycling head of medicine Dr Steve Peters, who was also Freeman's boss.
Last week, O'Rourke said that only Sutton would be called to the tribunal.
However, on Thursday she said Peters "might be able to assist us".
Sutton resigned from British Cycling in 2016 after being found to have used sexist language to former rider Jess Varnish.
In witness statements, Australian Sutton denied the testosterone was for him and denied knowledge of the delivery.
Following a General Medical Council (GMC) investigation, Freeman was charged with ordering testosterone to the National Cycling Centre in Manchester in May 2011 from Fit4Sport Limited in order to boost the performance of an athlete.
O'Rourke made a number of complaints in the early stages of proceedings on Thursday, which threatened to delay further the long-awaited tribunal which could reveal details about British Cycling and Team Sky, who enjoyed unprecedented success over the past decade.
The tribunal was postponed in February after Freeman cited ill-health. Legal arguments about the nature of the charge against Freeman delayed proceedings this week.
At the start of the hearing, O'Rourke said she was "very disappointed" after a GMC application to change Freeman's charges was granted.
In effect, it lessens the threshold for Freeman to be found guilty of ordering testosterone. Now the allegation against him does not surround his motive to supply athletes with the banned substance, but that he placed the order "knowing or believing" it was intended for athletes.
Freeman previously denied ordering the sachets in May 2011. Later that year he asked Fit4Sport for written confirmation the testosterone had been sent in error.
In the preliminary hearing last week, O'Rourke said her client will admit he had "told a lot of lies" but that his latest witness statement, submitted in September, is "the truth".
O'Rourke also said that Freeman was made to feel "anxious" and "very concerned" after raising questions about the tribunal's transparency.
She claimed that email correspondence between the GMC and the MPTS about witnesses was not shared with the defence.
British Cycling said in a statement: "It is in the public interest and in the best interests of the sport that the allegations against Dr Richard Freeman are heard and examined openly by the Medical Practitioners Tribunal Service.
"British Cycling is a co-referrer in this case and we will continue to support the General Medical Council's work as there remain historic questions to be answered."