Former career diplomat Maris Sangiampongsa is being tipped as the likely new foreign minister after Parnpree Bahiddha-Nukara resigned in a shock announcement on Sunday.
Mr Maris was an adviser to Mr Parnpree at the ministry and is widely expected to be his successor, according to media reports.
He was ambassador to Australia and to other countries before retiring while he was ambassador to Canada.
Matichon Online reported Mr Maris was assigned to work at Government House when Thaksin Shinawatra was prime minister. He has since maintained a close relationship with the Shinawatras.
Prime Minister Srettha Thavisin said earlier on Monday a new foreign minister had been selected but refused to provide details.
Mr Parnpree resigned on Sunday, effective immediately, in protest after he lost the post of deputy prime minister, which he held concurrently with foreign affairs, in the cabinet reshuffle.