Thanathorn Juangroongruangkit, the leader of the Progressive Movement and key supporter of the Move Forward Party (MFP), has been questioned if he has made a political deal with Thaksin Shinawatra, the de facto leader of the Pheu Thai Party.
Assoc Prof Somchai Preechasinlapakun, who is a Chiang Mai University law scholar, said that Mr Thanathorn owes other MFP supporters a clear answer whether he had recently negotiated a deal with Thaksin in Hong Kong.
"[Mr Thanathorn] remains tight-lipped about this very question, and this will only shatter confidence in the MFP's political direction," said Assoc Prof Somchai, who stated he voted for MFP in the May 14 general election.
"As a citizen of Thailand, I expect to see a straightforward political development, not another political game being played through secret negotiations," he said.
According to a Pheu Thai source, a political deal involving the forming of a new government was reached in Hong Kong between Mr Thanathorn and Thaksin, who has vowed to return to Thailand on Aug 10 after living in self-imposed exile for almost two decades.
Assoc Prof Somchai said if Mr Thanathorn didn't go to Hong Kong, he needs to dismiss the rumour; but if he did go and was involved in negotiations, he must explain why.
Responding to media reports about the alleged Hong Kong deal, Wiroj Lakkhanaadisorn, an MFP list-MP, tweeted that he didn't pay much attention to whether or not it was true.
"Even if I end up feeling like a fool when I realise I have been deceived and lost everything, my honesty and integrity will still be here with me. And I can still walk with my chin up and face anyone as usual," he said on Twitter.
"And even if this mission is doomed to fail because of betrayal, that will still be better than making it fail now due to distrust within the team."
Rangsiman Rome, another key list-MP for the MFP, declined to comment on the rumour, saying he wasn't in a position to comment as Mr Thanathorn doesn't hold a formal position in the MFP.
Attachak Satayanuruk, a history scholar at Chiang Mai University, said he thinks Thaksin's announced return to Thailand is part of a deal between him, Pheu Thai and a side that the scholar described as the ruling class.
These sides are in a deal due to their mutual fears that the MFP's reformist movement could threaten their political security, said Mr Attachak.
As a part of the deal, Thaksin will look for ways to divide the supporters of Pheu Thai and MFP as much as possible so as to stall the MFP's reformist movement, said Mr Attachak.