There is still "a wall of denial" within Russian athletics and its federation is not doing enough to prove it is ready to participate at this summer's Olympic Games in Rio, Dick Pound has said.
The Russian athletics federation was suspended from all international competition for doping offences in November after a meeting of IAAF council members.
Pound, chair of the World Anti-Doping Agency's independent commission, speaking at the Tackling Doping in Sport conference in London on Wednesday, said: "Even with the presence of credible evidence, there was, and to some extent there still is a wall of denial.
"Russia, in the sport of athletics, is on the outside trying to get back in. The onus is on it to justify any readmission.
"It is also clear that opinion is divided on the matter of readmission. The Russians seem to assume that the controversy will disappear and there should be no question regarding their participation in Rio. No question.
"In other parts of the sporting world there is great resistance to any fast-track solution."
Pound, who thought it was "unlikely" that the suspension of track and field athletes would be extended to other sports in Russia, added: "We said [to the Russian athletics federation] 'here are some of the findings you are going to be facing. If you want to get back in you have got a steep hill to climb, but if you devote all of your resources and attention to solving the problem instead of solving the report you have got a chance to do it in time for Rio'.
"I don't think they are devoting all their time and energy to where they should be to getting, or where they ought to be. They really have got to address the issues.
"It is a considerable hurdle for them and if the two organisations [WADA and the IAAF] are not satisfied that the clean competitors of the Games are protected then my guess is that they may not make it back for Rio."
The two-day Tackling Doping in Sport conference is taking place under the backdrop of five-time grand slam winner Maria Sharapova's positive test for a banned substance at this year's Australian Open tennis tournament.
"The fact of the matter is right now Russian athletics is suspended," Pound added. "Russia has to explain to Russians why it is that their track and field team may not be in Rio. Nobody is going to buy that it is a western plot.
"One of the accusations early on was that the reason we were so tough on Russia is that the whistle-blowers we trying to seek refugee status in Canada. It's absolute nonsense."
Meanwhile, WADA president Sir Craig Reedie called for greater funding from sports to tackle the issue of doping.
"Here we are awash with money and I am perplexed that the sport movement is reluctant to make the investment needed to protect clean sport," Reedie said.
"Clearly we have a lot to do. Will doping disappear in time? Of course it cannot be eradicated entirely because it is in some people's nature to cheat, but we can do our level best to reduce doping and make the risk outweigh the reward.
"We want to create a healthy sporting environment where doping is not an option."