Gaidar, one of the leaders of a liberal opposition party who served briefly as prime minister in the 1990s under President Boris Yeltsin, began vomiting and fainted during a conference on Irish-Russian relations Friday, and was rushed into intensive care at a hospital. Participants at the conference outside of Dublin said he had complained of feeling ill for much of the day.
"Doctors still can't figure out a reason for what happened," Maria Gaidar said in comments broadcast on Ekho Moskvy radio.
The 50-year-old economist returned to Moscow earlier this week, and doctors at a Moscow hospital considered his condition to be satisfactory, his spokeswoman Irina Sergeyeva told The Associated Press.
Russian news reports quoted Gaidar aides as saying there was no indication so far of foul play, but they gave no further details or possible reasons for his illness.
Gaidar's illness follows the poisoning of former KGB spy Alexander Litvinenko, who died in London just one day before Gaidar fell ill. Another former KGB spy who met with Litvinenko on the day he was allegedly poisoned, Andrei Lugovoy, served as Gaidar's bodyguard at one point.
Colm Keane, spokesman for National University of Ireland at Maynooth, where the conference was held, said that medics initially suspected Gaidar's diabetes or some sort of ailment caused his illness last week.
"Even though everybody was very conscious of the story coming from London (about Litvinenko) ... we always believed it to be entirely separate from what was going on in London," Keane said.
A spokesman for the Irish Department of Foreign Affairs, speaking on customary condition of anonymity, said "we have received no evidence of anything untoward about this. He was certainly well enough to travel back home."
Anatoly Chubais, a top Yeltsin-era government official and now head of the national electricity monopoly, said he suspected a link between Gaidar's illness, Litvinenko's death and last month's murder of investigative reporter Anna Politkovskaya.
"The theory of attempted poisoning, attempted murder should undoubtedly be considered seriously," Chubais told state-run Rossiya television. "The chain of deaths of ... Politkovskaya, Litvinenko and Gaidar would perfectly correspond to the interests and the vision of those people who are openly talking about a forceful, unconstitutional change of power in Russia as a possible option."
Chubais didn't name anyone, but his statement sounded like an allusion to Boris Berezovsky, a self-exiled Russian tycoon and arch-foe of the Kremlin who has talked about a possible forceful change of government in Russia. Berezovsky, who was given asylum in Britain, had close contacts with Litvinenko.
Russian lawmakers and politicians have suggested Berezovsky could have been behind the deaths of Politkovskaya and Litvinenko as part of a plan to blacken the reputation of President Vladimir Putin and the Kremlin.
Along with Chubais, Gaidar is best known for as the architect of the sweeping free-market reforms that were instituted in the early years of Yeltsin's administration. He is one of the leaders of the liberal opposition party Union of Right Forces and heads a think-tank called the Institute for the Economy in Transition.
Maria Gaidar is well-known as a liberal youth activist and vociferous Kremlin critic.