Prime Minister Prayut Chan-o-cha yesterday said he had no intention of delivering an incomplete oath during last month's cabinet swearing-in ceremony.
He made the comment during a visit to the southern province of Yala.
"It will be settled soon because I had no intention of doing it wrongly. Let's focus on the intention," the prime minister said.
Critics claim the prime minister did not vow to protect and abide by the constitution, which is the final paragraph in Section 161 of the charter.
This could render his cabinet illegitimate and unable to perform its duties, they say.
The Ombudsman decided yesterday to examine the legitimacy of the cabinet's oath following the omission, in response to a petition from an activist.
Raksagecha Chaechai, secretary-general to the Ombudsman, said the Ombudsman decided to accept the petition from activist Srisuwan Chanya who asked the Ombudsman to forward the issue to the Constitutional Court or the Administrative Court.
He wants a ruling on the legitimacy of the government based on the incomplete oath made before His Majesty the King on July 16.
The activist filed his complaint on Monday, questioning whether an incomplete oath was in breach of Section 161 of the constitution.
The Ombudsman's legal section will study the legal aspects concerning the issue and would decide if testimony is required from any concerned party, Mr Raksagecha said.
The Ombudsman had not yet decided whether the issue concerned either court.
"But the Ombudsman has guaranteed quick consideration of an issue that is important and of interest to society," he said.
On Monday, Mr Srisuwan said the last sentence was missing from the oath Prime Minister Prayut read out for cabinet ministers to repeat as was required by Section 161 of the constitution.
He accused the prime minister of not heeding the constitution and jeopardising the legitimacy of the government.
That could have serious legal and political consequences and deal a serious blow to 16 million people who voted for the constitution in the 2016 referendum, the activist said.
The opposition yesterday postponed its bid to have the premier explain the omission as Gen Prayut was on a trip to the deep South.
Pheu Thai Party leader Sompong Amornwiwat said the opposition would wait for the prime minister to return to provide an explanation before the House of Representatives.