"Sonthi has asserted that he staged the coup only to 'do his job' and has no intention to cling to power," said Chaturon, former acting leader of the defunct Thai Rak Thai Party.
However, if Sonthi decides to run in the next poll, it would show he actually wanted to gain power under the rules written for his control, Chaturon said.
Sonthi on Tuesday said he had not thought of his future after his retirement as Army commander-in-chief at the end of September, especially on whether he would run in the next election. He refused to comment more on the speculation.
Sonthi came under fire from critics and allies recently following rumours that he is planning to lead a new political party backed by the military in the next election. They believe Sonthi wants to cling to power.
Prasong, chairman of the Constitution Drafting Assembly, said Sonthi should have second thoughts if he is planning to jump into politics. He said the CNS chief would not be able to avoid fierce criticism that the September 19 coup to oust the government of Thaksin Shinawatra was only for his and his clan's benefits.
At the beginning, the people did not oppose the junta and the [military-installed] government, but they were later disappointed with them, Prasong said. Those new rulers should take the public sentiments seriously, he added.
Prasong said Sonthi should consider the propriety of the situation. He must resign as CNS chairman before running in the election. However, as the interim government and the CNS would be involved in conducting the election, doubts might rise over issues of fairness and transparency.
"The generals in the CNS have been speculating for a while about their intention to cling to power," Prasong said. Moreover, it was linked to the constitution drafting, which made the people doubt if the whole incident was part of a CNS plot to retain power, he said.
Prasong also cautioned Sonthi that after being a professional soldier throughout his career, he might be trounced by experienced politicians.
He said Sonthi had no need to be concerned if he would be the target of revenge attacks after his retirement. If the CNS chief wins the hearts of the whole nation by his sincerity to serve the people, the people and the soldiers would protect him from any future threats, he added.
Democrat secretary-general Suthep Thaugsuban struck a contradictory note and said Sonthi had every right to run his Lower House campaign.
"It would be a good sign if Sonthi would turn himself into a politician because that is the way of democracy. We should appreciate him [if he did it that way]. He is welcome," Suthep said.
"Every single person has the right to run in the election, no matter who they are - businessman, farmer, policeman or soldier. I haven't talked about the matter with him. But, in general, the Army commander-in-chief, government officials or ordinary people are welcome here at the Democrat Party," Suthep said.
Chat Thai Party leader Banharn Silapa-archa said Sonthi should be welcomed to join politics as he needed a "haven" to ensure he would not "get hurt" after leaving power.
Other political figures also weighed in on the issue on Tuesday, with some cautioning the CNS chief and urging him to think carefully before making the decision.
One of the Ruam Jai Thai group leaders, Anek Laothammatas, said the timing was not appropriate for Sonthi to be running in the coming election. Anek said Sonthi must hold the position of CNS chairman before the next government is formed. If he runs in the election, and has to step down from the CNS, another CNS chief would have to be appointed and problems could occur as a result of that.
Anek suggested Sonthi should wait for the next election.
Political scientist Chai-anan Samudvanija said party-list MP will be best bet for Sonthi should he want to enter politics. He said Sonthi should not establish a party and warned that "Being a party leader will be risky [for Sonthi]".
However, Democrat Party leader Abhisit Vejjajiva said it would be better for Sonthi to run in the election rather than pursue power in other ways.