A leaked US diplomatic cable obtained by the Wikileaks website says three influential figures in Thailand expressed concerns about the prospect of the crown prince becoming king.
Two of those mentioned are senior advisers to the king.
The cable was sent to Washington in January this year by the then American ambassador in Bangkok.
The ailing 83-year-old King Bhumibol Adulyadej is the world's longest-reigning current head of state.
The reverence in which the monarch is held is invariably evident whenever and wherever he appears in public.
Crown Prince Vajiralongkorn is in his late fifties.
The ambassador's cable quotes alleged conversations with General Prem Tinsulanonda, the head of the privy council, a former prime minister, Anand Panyarachun, and Air Chief Marshall Siddhi Savetsila.
It says all three had quite negative comments about the crown prince and two of them - while asserting that the crown prince will become king - implied that the country would be "better off if other arrangements could be made".
The cable also cited concerns about the crown prince's private life.
The ambassador's conclusion in the cable is that "on the two most difficult and sensitive issues of the day in Thailand - [ousted Prime Minister] Thaksin [Shinawatra] and the monarchy - the Thai elite appear as unsure about the future as any other sector of society".
He says the stakes are significant for all sides.
Analysts point out that these views are reported in a cable sent at the start of what has been one of the most turbulent years in Thailand's recent history.
Dr Tim Forsyth, an East Asia expert from the Development Studies Institute at the London School of Economics, told the BBC:
"The Wikileaks cables certainly give the impression that the members of the privy council of Thailand are concerned about the suitability of the crown prince. Of course these cables are unconfirmed and it is very difficult for outside people to comment on it.
"But it does seem to suggest that some of the origins of the political problems in Thailand over the last few years are somehow connected to this worry about what will happen to the monarchy.
Dr Forsyth said some people in Thailand had told him that the 2006 coup which sought to depose Thaksin Shinawatra as prime minister took place partly because they were worried about the relationship between him and members of the royal family.
"This might suggest," Dr Forsyth said, "that this underlying uncertainty about the royal family might be part of the political problems going on in Thailand over the last few years, such as the riots in Bangkok earlier this year."
There has been no comment so far from those cited in the leaked US cable, including the crown prince.
Thani Thongpakdi, foreign ministry spokesman, said: "Regarding documents that have been released by Wikileaks in general, Thailand is not in a position to confirm the accuracy or authenticity of such documents because they were not issued by us.
"Additionally many documents seem to be conveying hearsay or gossip which in some circumstances may have been reported out of context. We should therefore not give credence to them."
Correction 19 December: This article has been amended to clarify that Air Chief Marshall Siddhi Savetsila has never served as prime minister of Thailand.