Investors and business leaders are increasingly worried that the probe into the Russian oil giant will shake the relative stability that Mr. Putin has brought to Russia since he came to office in 2000.

Russian media reported that Alexander Voloshin, chief of staff to President Putin, resigned after the arrest. If confirmed, his departure would mark the strengthening of a faction in the Kremlin that has pushed for tighter state control of the economy and society, the newspaper says.

For its part, the Russian newspaper Izvestia reports, quoting its sources in the Kremlin, that Mr. Voloshin will resign later this week. According to the newspaper, Mr. Voloshin first tendered his resignation when the conflict with law-enforcement agencies started. He tendered his second resignation in July, after the arrest of Platon Lebedev, a co-chairman of YUKOS, and the third one – after Mr. Khodorkovsky’s arrest.

The Izvestia names three possible successors. One of them is Vladislav Surkov, one of the leading spin doctors in the country. He is quite pragmatic and liberal-minded, and has a good command of today’s political trends. In the presidential administration, he is responsible for Chechen affairs and the State Duma.

The second candidate is Dmitry Medvedev, a member of so-called ‘Putin’s team’. His position is neutral, not linked to the law-enforcement bloc. Mr. Voloshin’s Senior Deputy, Mr. Medvedev has been seen as his successor.

And the third candidate is Igor Shuvalov. He is Mr. Putin’s aide and an experienced bureaucrat.