Len Blavatnik, who is suing JPMorgan Chase over claims it lost 10 percent of the $1 billion it managed for him, refused to extend the fact-gathering period as requested by a bank lawyer about to have open-heart surgery, the lawyer said.

Bruce Birenboim, an attorney for JPMorgan, explained Blavatnik's refusal in a letter to a Manhattan judge last week. Birenboim said Blavatnik wouldn't extend the schedule two months to June 29, a request Birenboim made because he will be unavailable for six to eight weeks.

"I have never in my 30 years of practice found an adversary's position to be so unprincipled and unprofessional," Birenboim, a partner at Paul, Weiss, Rifkind, Wharton & Garrison, wrote to New York State Supreme Court Justice Melvin L. Schweitzer.

Blavatnik, 54, sued in 2009, claiming that New York-based JPMorgan, the biggest U.S. bank by assets, put twice as much money into risky mortgages as his investment guidelines allowed. Blavatnik says the bank lost $98 million of his funds.

Blavatnik, born in Ukraine, runs New York-based Access Industries Group, which owns energy, media and real estate companies. Blavatnik is worth $9.5 billion, according to Forbes. Blavatnik bought Warner Music Group from Edgar Bronfman last year.