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 time as premier has already ended.
Mr Chaikasem, the Pheu Thai's chief strategist, is the party's only remaining choice to compete for the premiership in parliament, according to Pheu Thai leader Dr Cholnan Srikaew.
The two previous candidates, Chadchart Sittipunt and Khunying Sudarat Keyuraphan have left the party to pursue other political endeavours, he said.
Mr Chadchart severed ties with Pheu Thai to run for the Bangkok governorship. He won the race in May.
Khunying Sudarat quit the party and founded the Thai Sang Thai Party.
The departure of the two politicians has left Mr Chaikasem as the party's only choice for prime ministerial candidate.
Dr Cholnan said Pheu Thai will throw Mr Chaikasem's name into the hat if it is determined by the Constitutional Court that Gen Prayut's eight year tenure 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 loses his prime ministerial post, parliament will need to find his replacement by going back to the names of prime ministerial candidates proposed in the last general election in March 2019.
Apart from Mr Chaikasem, Anutin Charnvirakul, leader of the coalition Bhumjaithai Party is also among the valid prime ministerial candidates.
Dr Cholnan said Mr Anutin has a chance of succeeding Gen Prayut as prime minister although he admits there has been talk of Deputy Prime Minister Prawit Wongsuwon, who is currently acting prime minister, being nominated as a prime minister candidate from outside the 2019 candidacy list.
But the candidates on the list would be voted on first. If none garnered enough votes to be prime minister, a candidate not on the list would be nominated and voted on by both MPs and senators. However, an outsider candidate would need the support of at least two-thirds of parliamentarians, or 488, to become prime minister.
Dr Cholnan said a House dissolution cannot be ruled out. In which case, a general election would be called.
Even if Gen Prawit took over from Gen Prayut as prime minister, the political landscape would be unchanged, he added.