Former career diplomat Maris Sangiampongsa has been tipped as the likely new foreign minister after Parnpree Bahiddha-Nukara's shock resignation announcement on Sunday.
Mr Maris was an adviser to Mr Parnpree at the ministry and is widely expected to be his successor.
He had been Thailand's ambassador to Australia, Nepal and other countries before retiring as ambassador to Canada.
Mr Maris was assigned to work at Government House when Thaksin Shinawatra was prime minister about two decades ago and has since maintained a close relationship with the Shinawatra family.
"Mr Maris has a wealth of experience in foreign affairs. He has maintained political ties with the Pheu Thai Party for a long time," a source told the Bangkok Post.
Mr Parnpree quit on Sunday, effective immediately, in protest after he lost the post of deputy premier, which he held concurrently with foreign affairs minister, in the reshuffle.
On Sunday, Mr Parnpree said his resignation was to ''uphold the principle" that he should have total support for his work in both roles.
He said holding just the foreign ministerial post could hinder his work in international affairs and that there were other qualified candidates to assume the role.
Prime Minister Srettha Thavisin said yesterday that a new foreign minister had been selected to replace Mr Parnpree but refused to provide details.
The prime minister did not name Mr Parnpree's successor at the ministry, saying only that it was a person who had been working behind the scenes on foreign policy for the Pheu Thai Party.
Their qualifications would have to be examined before the new minister's name was forwarded to His Majesty the King for royal endorsement, Mr Srettha added.
In the reshuffle, Mr Parnpree was stripped of his deputy prime minister's portfolio but retained the post of foreign affairs minister. However, he tendered his resignation to the prime minister on Sunday.
The prime minister defended the decision, saying it allowed Mr Parnpree to take full control of foreign affairs after deputy foreign minister Jakkapong Sangmanee was moved to the post of PM's Office minister.
"Currently, there are already six deputy prime ministers, which I believe should be enough. It is impossible for every cabinet minister to serve as deputy prime minister concurrently,'' Mr Srettha said.
Mr Srettha admitted he had not expected Mr Parnpree to step down and apologised if the change left him dissatisfied.
Commenting on the cabinet reshuffle, Stithorn Thananithichot, director of the Office of Innovation for Democracy at King Prajadhipok's Institute, noted that many people who have worked closely with the Pheu Thai Party have been appointed as cabinet ministers.
"For Pheu Thai, the party takes precedence over individual members. The cabinet reshuffle may have left some disappointed ... but it is unlikely that they will defect to other parties," Mr Stithorn said.
He also noted that whenever it becomes the government, Pheu Thai has always overseen the Foreign Affairs Ministry since its two previous incarnations -- the Thai Rak Thai Party and the People's Power Party -- both of which were dissolved for electoral fraud.
Chulapong Yukate, a Move Forward Party list MP who serves as deputy chairman of the House committee on foreign affairs, said yesterday that it was a shame Mr Parnpree had resigned as foreign minister, considering his capabilities and experience.
Durng the past seven months, Mr Parnpree had carried out his duties as foreign minister remarkably well, according to Mr Chulapong.
He said the prime minister should appoint someone who is qualified to become Mr Parnpree's successor quickly to handle several issues that require urgent attention, such as the fighting between the Myanmar military and rebel forces and measures to cope with an expected influx of refugees fleeing across the border.