Former Russian acting Prime Minister Yegor Gaidar is being treated in a Moscow hospital amid rumours about the cause of his mystery illness.
Mr Gaidar was rushed to intensive care after collapsing in Dublin
Mr Gaidar became violently ill during a visit to Ireland last week, and his daughter Maria told the BBC that doctors believe he was poisoned.
Irish police are investigating the claims, as he recovers in Moscow.
Mr Gaidar, 50, fell ill a day after Russian ex-spy Alexander Litvinenko died of radiation poisoning in London.
Mr Gaidar briefly served as prime minister in 1992 under Russian President Vladimir Putin's predecessor, Boris Yeltsin.
He now heads a Moscow-based think-tank which has criticised President Putin's economic policies, but he is a marginal political figure who is not regarded as a prominent political opponent of the Russian leader.
'Pale and thin'
Mr Gaidar suffered from a nose bleed and vomiting before fainting in Dublin last Friday, during a visit to promote his book The Death of Empire: Lessons for Contemporary Russia.
Ms Gaidar was quoted as saying her father had eaten a "simple breakfast of fruit salad and a cup of tea".
June-Dec 1992: Russian acting prime minister
Implemented economic "shock therapy"
Director of Institute for the Economy in Transition
Ms Gaidar, an anti-Kremlin activist, told the BBC doctors in Moscow had been unable to find any other cause except poisoning.
"The doctors think that they don't find any other reason of his condition that he was poisoned with some strange poison they cannot identify," she said. "But to have an official conclusion they're still waiting for the information of the doctors of Dublin."
She said that if her father had been deliberately poisoned "it could be a political poisoning because there are no personal or business reasons why someone would want to do that".
She told Reuters news agency her father was speaking, but looked pale and thin.
Mr Gaidar was treated in intensive care in Dublin after he collapsed, before being flown to Moscow.
The Irish government has said it had no reason to believe there was anything untoward about Mr Gaidar's illness.
However, the police force said it was investigating Mr Gaidar's movements during his trip.
"Enquiries to date have been conducted with hospital and medical staff and through the diplomatic corps," a police statement said.
"Public health and safety is of paramount importance and there is nothing known which indicates that any member of the public is at risk."
As acting prime minister, Mr Gaidar was responsible for introducing sweeping economic reforms following the collapse of the Soviet Union.
His programme of economic "shock therapy" under which price controls were lifted and large-scale privatisations were launched angered many Russians who saw their savings devalued.