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, and two former prime ministers, 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. BBC News
