Thaksin, a former telecoms tycoon who became prime minister in 2001 and ousted by the military in 2006, has towered over Thailand's politics despite having lived in self-imposed exile since 2008 to avoid graft convictions which he said were politically motivated after his government were ousted in a 2006 coup.

On Saturday, Thaksin said in a post on X, the social media platform formerly known as Twitter, that he needed a medical check up and would delay his return, originally planned for Aug. 10, by "a couple of weeks".

Thaksin's backed Pheu Thai Party came second in the May election after the progressive Move Forward Party.

The two election winning parties have been trying to form a government with six like-minded partners but have been blocked by the Senate, dominated by military appointees, and conservative opponents.

Earlier this week, Pheu Thai took the lead in trying to form a government without Move Forward, whose own attempts to form a government met with relentless opposition from the pro-military conservatives alarmed by its reform agenda. read more

The constitution, drafted during military rule, requires a joint sitting of the elected Lower House and the appointed Senate to vote for a prime minister.

Move Forward has twice sought to have party leader Pita Limjaroenrat endorsed as prime minister by the two houses of parliament, but was blocked both times despite winning the most seats in the election.

Pheu Thai said earlier this week that it would nominate Srettha Thavisin, a real estate magnate, as its prime ministerial candidate, and parliament had been set to vote on his candidacy on Friday.

But, that vote was postponed pending a Constitutional Court review, due on Aug 16, of the parliamentary proceeding that blocked Pita's renomination for the vote the second time.