Yegor Gaidar, architect of Russia's market reforms, was being treated in a Moscow hospital yesterday for a mystery illness that one of his associates said may have been inflicted on him deliberately.
Doctors at one point feared Mr Gaidar, 50, a former acting prime minister who is now a veteran of the liberal opposition, could die after he collapsed during a visit to Ireland to present his new book, "Death of the Empire."
Anatoly Chubais, a close former colleague who heads Russia's state electricity monopoly, said someone may have stood to gain if Mr Gaidar had suffered the same fate as Alexander Litvinenko, a Russian former spy who died from poisoning in London.
"He lost consciousness for three hours and was taken to intensive care for a long time where doctors were fearful for his life," Mr Gaidar's daughter Maria, an opposition activist, said.
"He is in Moscow and doctors are trying to come up with a diagnosis but they can't find one. His condition is satisfactory and he is speaking but he looks very bad - he looks pale and thin."
She said doctors were trying to diagnose "rather strange symptoms" including a nose bleed and loss of consciousness, but she did not want to comment on suggestions he had been poisoned.
Yegor Gaidar's programme of shock therapy under President Boris Yeltsin helped dismantle Communist economic management but also angered millions whose savings were devalued.
Mr Gaidar has made restrained criticism of Mr Putin's economic policies. Now head of the Moscow-based Institute for the Economy in Transition, he fell ill a day after Mr Litvinenko died in London from radiation poisoning.
Mr Litvinenko, a critic of the Kremlin, left a letter blaming Russian President Vladimir Putin for his death. The Kremlin denies any involvement.
Mr Chubais drew a parallel between Mr Gaidar's illness, Mr Litvinenko's death and Anna Politkovskya, an outspoken investigative reporter who was shot dead in Moscow in October.
"Yegor Gaidar on 24 November was in the balance between life and death. Could this be simply some sort of natural illness? According to what the most professional doctors, who have first-hand knowledge of the situation, say - no," Mr Chubais said.
Mr Chubais, the target of an assassination attempt in 2005, said he did not believe Mr Gaidar's illness was the work of intelligence agents working for Mr Putin.
But he said: "For me there is no doubt that the deathly Politkovskaya-Litvinenko-Gaidar chain, which by a miracle was not completed, would have been extremely attractive for the supporters of an unconstitutional, forceful change of power in Russia."