ONeill was among a small group of directors who urged Citigroup to consider the benefits of splitting the bank after the global financial crisis.
But he has concluded that breaking up Citigroup would not make sense now, given economic and regulatory uncertainty, the Journal quoted the people as saying.
Citigroup spokesman Ed Skyler declined to comment on the Journal story, but noted that ONeill had said in October that directors were confident in the companys current strategy.
Also, new chief executive Mike Corbat said in December that the company saw its global footprint as a competitive advantage.
Citigroup had considered splitting during the financial crisis, but decided instead to place hundreds of billions of dollars worth of assets into a separate unit where they are being sold or wound down.
ONeill wanted to look at the option when he joined the Citigroup board in 2009, but was blocked by then-chief executive Vikram Pandit, who did not want to consider the option, the Journal report cited the people as saying.
Late last year, Citigroup said it was cutting 11,000 jobs worldwide, or 4% of its workforce.
ONeill, 66, has a history of ruthlessly shedding businesses that are not earning enough money.