Caretaker Prime Minister Prayut Chan-o-cha has spoken against a proposal by some allies of the Move Forward Party (MFP) to wait 10 months for an end to senators' tenure before forming a new government.
"I don't think it's appropriate," Gen Prayut said in response to reporters' questions about the idea.
He gave his brief answer only after reporters repeated the question a second time when he arrived at Government House on Tuesday morning.
Gen Prayut announced his retirement from politics earlier this month.
The Thai Sang Thai and Fair parties have proposed the eight coalition allies wait for the five-year term of the military-appointed Senate to end in May next year, so the MFP alliance could conveniently have its prime ministerial candidate elected by the House of Representatives alone.
The MFP won the most seats in the May 14 general election, with 151. The Pheu Thai Party came second with 141 MP seats. They are the core of the alliance, which has a 312 majority in the 500 seat elected House.
The current 249 senators (one recently resigned) are entitled to take part in the vote for the new prime minister, together with the elected representatives. The new prime minister needs a majority of the two chambers, at least 375 votes.
On July 13 Mr Pita, the then sole candidate for prime minister, was rejected by the joint sitting, receiving only 324 supporting votes including only 13 from senators, most of whom abstained.