Future Forward Party leader Thanathorn Juangroongruangkit has revealed that Pheu Thai offered to nominate him for prime minister if that party's own candidates for the job fail to get into parliament.
He said he replied it was not a condition for joining the coalition.
The autoparts tycoon revealed on Thai Rath TV on Wednesday night that Pheu Thai chief strategist Khunying Sudarat Keyuraphan had made the offer during a conversation on Sunday night.
It came after unofficial results from the poll showed Pheu Thai was likely to win more constuency seats than the Palang Pracharath Party. But Pheu Thai would not get any party-list seats under the complex seating formula, if the number of constituency seats it gets equals or exceeds the maximum seats a contesting party can get from the election - which is likely to be the case.
The formula involves dividing the total number of votes cast nationwide by the 500 seats in the House, effectively limiting the number of seats any single party can gain.
Pheu Thai proposed three candidates for prime minister - Khunying Sudarat, Chaikasem Nitisiri and Chadchart Sittipunt. Khunying Sudarat and Mr Chaikasem were second and third respectively on the party-list sent to the Election Commission. Mr Chadchart opted out of the contest.
"If the Future Forward Party wants the prime minister to be a member of the House, [Future Forward] can take the position," Mr Thanathorn quoted Khunying Sudarat as saying.
Mr Thanathorn said he declined the offer and told the Pheu Thai chief strategist that the prime ministership was not a condition of Future Forward joining a coalition to form a government.
Future Forward has demanded the next prime minister be an elected member of the parliament .
Mr Thanathorn said the priority was to end the National Council for Peace and Order's hold on power. Khunying Sudarat had intended to be an MP, but the seating formula could see her miss out, he added.
The two had talked on the phone on Sunday as Pheu Thai began its move to form a prospective coalition government.
Pheu Thai announced an alliance of seven parties, including Future Forward, on Wednesday.
Pheu Thai is expected to end up with 137 constituency seats, followed by Palang Pracharath with 97. Future Forward has 30 seats, according to unofficial results.
Future Forward could benefit the most from the party-list, with about 50 extra seats. Palang Pracharath will also increase its numbers, but with fewer party-list MPs.
