His absence from the political scene comes  at a critical time  as Yevgeny Primakov, prime minister, completes the formation of his government  and tries  to set the country on a new course. 

Mr. Yavlinsky, 46,  first publicly proposed Mr. Primakov as a prime ministerial candidate, has seen his political fortunes rise in recent weeks, drawing support from some of Russia's most powerful business leaders. 

An opinion poll by the VTsIOM polling agency over the weekend, showed Mr. Yavlinsky, leader of  the Yabloko party, closing the gap on other presidential contenders. Mr. Yavlinsky won 12 per cent putting him just behind Yuri Lizhkov, Moscow's populist mayor, with 13 per cent. 

Gennagy Zyuganov, the communist party leader, and Alexander Lebed, the general-turned-governor of the Siberian region of Krasnoyarsk, came out  top   with 17 per cent apiece. 

A former amateur boxer who appeared to be in robust health, Mr. Yavlinsky was taken ill last Friday and admitted himself to hospital. His condition was "satisfactory" according to the Yabloko press service. 

Earlier on Friday, Mr. Yavlinsky had warned of a "very deep moral crisis" which had to be resolved by the country's leadership if Russia  were to avoid civil unrest. 

"Revolutions in this country happen not when there are economic crisis but when, as in 1917 and 1991, people reject power and say  No  to the authorities," he said in interview with the Financial Times. 

Mr. Yavlinsky said he had rejected an offer by Mr. Primakov to join the government as deputy prime minister in charge of social affairs.  Mr. Yavlinsky said he did not  want to be isolated  "decoration" in the cabinet and would only join the government alongside  a team of 10-15 Yabloko MPs, who could make a real difference to economic reforms. 

Mr. Yavlinsky, who came fourth in the first round of the 1996 presidential elections, said he aiming to doubled Yabloko's representation in Russia's 450-seat parliament to about 100 seats in next year's elections.