Russian billionaire Roman Abramovich hit back against fellow oligarch Boris Berezovsky on Monday, telling a court he was never the older man's protege and does not owe him a cent.

Berezovsky is suing Abramovich in a London court for several billion dollars, saying that Abramovich had intimidated him into selling shares in their jointly owned oil company Sibneft at a fraction of their value.

Abramovich, the media-shy owner of the Chelsea Football Club, dismissed that claim as nonsense as he took the stand at London's Commercial Court. The case has fascinated the city's large Russian community and provided a peek into the Wild West years that followed the 1991 collapse of the Soviet Union.

Abramovich told the court that he had never made a "legal, binding agreement" with Berezovsky over Sibneft, a Russian oil and gas conglomerate.

And in a written witness statement, he said Berezovsky "has already obtained a very substantial sum of money from me and I do not believe that he has any entitlement to be paid anything more, whether in law or honor."

Berezovsky, who amassed a fortune during Russia's privatization of state assets in the early 1990s, has testified that during the chaotic years after the breakup of the Soviet Union he was a mentor to Abramovich and treated him like a son. Together with a third partner they set up Sibneft.

But Berezovsky, an ally of former Russian President Boris Yeltsin, fell out with Yeltsin's successor, Vladimir Putin, shortly after he became president in 2000. Berezovsky fled to Britain, which granted him political asylum, and has since become a fierce critic of the Kremlin.

Abramovich sold Sibneft to Russia's state-owned gas monopoly Gazprom in a multibillion-dollar deal in 2005.

Abramovich, 45, said in his witness statement that "I was not his protege and he was not my mentor."

He claimed Berezovsky, now 65, was a political godfather whom he paid for protection. Abramovich used the Russian word "krysha," or roof, to describe their relationship.

"A person giving krysha to another was a person who acted as a protector," Abramovich said in his witness statement. "I had to pay Mr. Berezovsky for the opportunity of creating the oil company under his protection."

Abramovich's lawyer has said that between 1995 and 2002, the younger man paid Berezovsky $2 billion for his patronage, including money for homes in France, private planes, art works and jewelry.

"At times it was difficult to meet Mr. Berezovsky's demands and I thought they were often excessive. However I was concerned about what might happen if we lost the krysha," Abramovich said in his statement. "If Mr. Berezovsky needed to charter a plane in order to fly somewhere, or wanted a yacht to be chartered, he would ask me to pay for it."

Abramovich described Berezovsky as an intensely ambitious man with "far-reaching political ambitions."

"There was at times something of a megalomaniac about him that could lead to fantastic suggestions on his part," Abramovich said, citing one idea to restore monarchy in Russia.

"The grander the plan he entertained at any given time, the more cash he would be after in his almost-fanatical zeal to seek to make those grand plans a reality."

The case is expected to last for two months.