Mr Nattawut said he believed the nine have been picked by the People's Democratic Reform Committee as potential candidates for the post of "neutral" prime minister under Section 7 of the constitution.
Speaking in a programme on red-shirt TV station Asia Update, Mr Nattawut said the favourite candidates are Palakorn Suwannarat, a privy councillor, Gen Prawit Wongsuwon, a former defence minister and army chief, and Anand Panyarachun, a twice former prime minister.
The next two most likely alternatives are MR Pridiyathorn Devekula, a former deputy prime minister and finance minister, and Somkid Jatusripitak, also a former deputy prime minister and finance minister, he said.
According to Mr Nattawut, there are also three "dark horse" candidates - Surakiart Sathirathai, a former deputy prime minister and foreign minister, Asa Sarasin, a former foreign affairs permanent secretary and foreign minister, and Vikrom Kromdit, chief executive of the AMATA Corporation.
If there was a military coup army chief Gen Prayuth Chan-ocha would be the preferred candidate, he said.
Mr Nattawut argued that any attempt to install a "neutral PM" would be illegal.
"If any of them happens to be made prime minister, he should not be called 'Section 7 PM', 'neutral PM', or a 'decent PM', but should be called 'illegal PM', since no law backs them being in the position," Mr Nathawut said.
He added that there was also another man who would do anything to be the "neutral PM."
"That man is Abhisit Vejjajiva," he said.