The main opposition Pheu Thai Party will nominate Chaikasem Nitisiri for prime minister should the Constitutional Court rule at the end of the month that Gen Prayut Chan-o-cha's term of office has already ended.
Mr Chaikasem, Pheu Thai's chief strategist, is the party's only remaining choice to stand for the premiership in parliament, according to Pheu Thai leader Cholnan Srikaew.
The two other previously named candidates, Chadchart Sittipunt and Khunying Sudarat Keyuraphan, had left the party to pursue other political endeavours, he said.
Mr Chadchart severed ties with Pheu Thai to run for Bangkok governor. He won the race in May. Khunying Sudarat quit the main opposition party and founded the Thai Sang Thai Party.
The departure of the two politicians left Mr Chaikasem as the party's only option for a prime ministerial candidate.
Dr Cholnan said Pheu Thai will throw Mr Chaikasem's name into the hat if the Constitutional Court rules that Gen Prayut's eight years as prime minister, served in two back-to-back terms, are up. The court has announced it will rule on the matter on Sept 30.
If Gen Prayut is forced to step aside as prime minister, the parliament must find his replacement from among the names of prime ministerial candidates proposed by parties at the last general election in March 2019.
Anutin Charnvirakul, leader of the coalition Bhumjaithai Party, is among the valid prime ministerial candidates.
Dr Cholnan said Mr Anutin has a chance of succeeding Gen Prayut as prime minister.
He admitted there had been talk of Deputy Prime Minister Prawit Wongsuwon, who is currently acting prime minister, being nominated as a candidate for prime minister from outside the 2019 candidacy list.
But the candidates on the list would have to be voted on first. If none garnered enough votes to be prime minister, a candidate from outside the list would be brought in and votes cast by both MPs and senators. An outsider candidate would need the support of at least two-thirds of parliamentarians, or 488, to win the prime ministerial nomination.
Dr Cholnan said a House dissolution cannot be ruled out. In which case, a general election would be called.
If Gen Prawit took over from Gen Prayut as prime minister, the political landscape would be unchanged, he said.
The Pheu Thai leader insisted his party would never form a government with the ruling Palang Pracharath Party, citing differences in political ideology.
