* Onexim CEO replaced on RUSAL board by Onexim's deputy CEO
* Onexim CEO quit due to other business commitments - RUSAL (Adds quotes from a source close to Rusal)
MOSCOW Nov 13 (Reuters) - Russian tycoon Oleg Deripaska appears to have tightened his grip on aluminium giant RUSAL after seeing off the chief executive of rival shareholder Onexim, who has left the board.
RUSAL said on Tuesday Dmitry Razumov was replaced on the board by Christophe Charlier, Onexim's deputy CEO, due to other business commitments. Razumov said he did not have any disagreement with the board, RUSAL said in a statement.
Shareholders in RUSAL, controlled by Deripaska, have been in dispute over the company's corporate governance and its strategy over a 25 percent stake in Norilsk Nickel, the world's largest nickel and palladium miner.
"RUSAL's board decides nothing now and turned out to be a body which is signing off Deripaska's decisions," a source close to Onexim told Reuters on Tuesday.
A spokesman for Onexim, an investment vehicle of tycoon Mikhail Prokhorov, declined to comment.
Earlier this year, RUSAL's minority shareholder Viktor Vekselberg quit as the company's chairman, saying the firm was in "deep crisis" and overburdened with debt.
Deripaska has resisted calls to dispose of RUSAL's stake in Norilsk Nickel to pay down debts at a time when aluminium markets are weak. Onexim has been in favour of selling the stake, sources have said previously.
In October Matthias Warnig, a former East German secret agent turned investment banker who has known Russian President Vladimir Putin since the 1990s, was appointed chairman of RUSAL.
The source added that this decision did not change Onexim's strategy towards RUSAL, in which it owns 17.02 percent.
Meanwhile, a source close to RUSAL, said that Charlier attended several RUSAL board meetings as Onexim's representative recently because Razumov was busy with other projects.
"The current chairman of the board Matthias Warnig pays a lot of attention to discipline and demands that all members of the board attend the meetings," the source close to RUSAL said.
"Razumov is busy with a lot of projects and was often unable to attend the meetings," he added. "Charlier attended the meetings instead of him. The replacement of the Onexim representative only formalises the existing state of affairs."
RUSAL, which posted on Monday a recurring net loss of $76 million for the three months ended September, has negotiated waivers on tests of its loan agreements until the end of 2013.
Its net debt of $10.7 billion partly stems from the purchase of the Norilsk stake in 2008 for an estimated $14 billion. (Reporting by Polina Devitt; Editing by Mark Potter and Mike Nesbit)