The voices in a clip posted on YouTube purportedly said to be that of former prime minister Thaksin Shinawatra and Gen Yuthasak Sasiprapa are likely to be real, Green Group coordinator Suriyasai Katasila said on Sunday.
Mr Suriyasai, a former core member of the anti-Thaksin People's Alliance for Democracy, said the release of the clip and the timeline were well in line with current political developments.
The conversation reaffirmed that Thaksin was persisting with his plan to return to Thailand without having to take any punishment for his wrongdoing.
In the past, Thaksin had tried to push through his plan with help from Chalerm Yubamrung and the red shirts but failed.
He moved Mr Chalerm to the Labour Ministry after the failure, and started over with the plan by using Gen Yuthasak.
According to the plan, he said, the government would take complete control of the armed forces and issue an executive decree to grant amnesty for Thaksin without being obstructed by the military.
"The fifth reshuffle of the Yingluck (Shinawatra) cabinet happened after the two met and discussed matters as heard from the clip. The clip had definitely not been doctored.
"Gen Yuthasak is required to convince the people that such a plan does not exist and that he has not taken an assignment from Thaksin to interfere in and take complete control of the armed forces.
"He cannot simply deny that clip is not real," Mr Suriyasai said.
Mr Suriyasai said the armed forces are also required to convince the people that they would not be a tool for Thaksin.
The clip and images which had been released were believed to be the result of unsettled conflicts of interest in the government, he added.