NEW YORK (Bloomberg) — Bermuda- based MF Global Ltd., the derivatives broker whose chief executive officer quit last week, rebuffed a partnership offer by Interactive Brokers Group Inc., saying it didn't fit with the company's future plans.

Interactive Brokers CEO Thomas Peterffy offered MF Global his company's trading and risk-management systems in return for the use of the broker's sales force, a partnership known as an introducing-broker arrangement. MF Global, whose stock skidded almost 90 percent this year, rejected the offer days after receiving Peterffy's letter this week.

"It has no validity for our business model," MF Global spokeswoman Diana DeSocio said, declining further comment. Peterffy declined to comment on MF Global's reaction.

Former MF Global CEO Ken Davis resigned on October 29 after 17 years with the company.

He was replaced by former Chicago Board of Trade CEO Bernard W. Dan.