Human Rights Watch says gag orders have been imposed on the deposed leader's lawyers and information on her trial is hard to come by.
Myanmar's deposed leader Aung San Suu Kyi was due to give evidence on Tuesday in her trial that her supporters say is politically motivated.
Information on the trial has been hard to come by as Myanmar's military rulers continue their crackdown on dissent.
Gagging orders have been imposed on Suu Kyi's lawyers to prevent them from speaking to the media.
"There has been a conscious effort to keep reporting from the trial from getting out into the wider community," Phil Robertson, Deputy Asia Director for Human Rights Watch, told Euronews. "This is a serious abridgement of 'free and fair trial' standards that we're seeing going on now in Naypyidaw."
It comes as an ASEAN summit of Southeast Asian leaders takes place without Myanmar after the country's top general, Min Aung Hlaing, was barred from the meeting in protest at last February's military coup.
The only first-hand accounts of proceedings in the trial, which began in June, have come from her lawyers and co-defendants. Sessions are closed to reporters and the public and the trial has not been covered by state-controlled media.
The most serious charges against Suu Kyi are corruption, for which each count is punishable by up to 15 years in prison, and violating the Official Secrets Act, which carries a maximum term of 14 years. Her supporters and analysts say the military's aim using concocted charges is to put an end to her political career and stifle the National League for Democracy (NLD) movement.
Last week there were jubilant scenes as people detained for protesting against military rule were freed from prison. Myanmar's junta said several thousand would be released under an amnesty.
But some were promptly rearrested, others remain in jail and the government faces a growing insurgency in many parts of the country. Security forces have been blamed for the deaths of almost 1,200 civilians.
Watch the interview with Phil Robertson of Human Rights Watch in the video player above.