Eduard Khudainatov was appointed as acting president of Russia's top state-run oil company Rosneft, the company said on Friday.
Khudainatov used to be the company's first vice president, the company said in a statement.
A contract with the company's former President Sergei Bogdanchikov expired on June 29 and rumours have said it will not be resumed. But Bogdanchikov rejected the rumours earlier this week.
A Rosneft spokesman told RIA Novosti news agency that Bogdanchikov was on a business trip, which caused the necessity of appointing acting president.
But a Rosneft source said that Bogdanchikov was on holiday from Friday.
"Nobody officially spoke about the resignation, nobody informed the staff. Now there are two acting presidents - Bogdanchikov and Khudainatov.
Today Khudainatov has congratulated company employees with the Oil worker Day not on behalf of Bogdanchikov, but on behalf of Board Chairman (and Russia's Vice President Igor) Sechin," the source said.
Rumours about Bogdanchikov's resignation appeared on the market in summer 2009 following an amendment to the company's charter, which said the president may be appointed by the board of directors and not by a shareholders' meeting.
Deputy Energy Minister and former Rosneft employee Sergei Kudryashov, Khudainatov and Rosneft First Vice President Pavel Fedorov are mentioned as Bogdanchikov's possible successors.