Justin Rose holds the 54-hole lead by 1 shot over Rory McIlroy and Xander Schauffele. Tiger Woods is tied for 11th, 5 strokes back.
The course has had in excess of 3 inches of rain for the week, according to Slugger White, vice president of rules and competition for the PGA Tour.
"We've got teeing grounds that are very marginal, and we've got fairways that are very marginal. We obviously need it to stop right now so we have two to two and a half hours to let it drain down and get the maintenance crew out there to see if we can push some water around."
That break in the weather never happened Sunday.
The plan for Monday is to tee off at 7:30 a.m. ET in threesomes off both tees, with the last group going off at 9:20 a.m. White said that according to the PGA Tour's regulations, every effort is made to play 72 holes. But unless at least half of the 69-player field completes the final round by Monday, the tour would not extend the event to Tuesday.
"Nor would we start a round on Monday thinking we could not get half the field finished," he said.
If the event is shortened, Rose would be the winner and full World Ranking points, FedEx points and prize money would be allotted to the field.
But not getting a final round would obviously affect several players who are trying to finish among the top 30 in points and advance to the season-ending Tour Championship that begins Sept. 20.
Among them is 2015 FedEx champion Jordan Spieth, who would end up 31st in the standings and miss the Tour Championship for the first time since turning pro and playing a full season in 2013.
Keegan Bradley is 30th and would be exempt for the first three major championships in 2019.
Emiliano Grillo, Andrew Putnam, Ryan Armour and Chez Reavie hold down the 31st through 35th positions.
Bryson DeChambeau, who won the first two FedEx events at the Northern Trust, is assured of leaving the BMW Championship atop the standings heading to Atlanta. Rose, Justin Thomas, Dustin Johnson and Tony Finau would hold the next four spots and be assured of winning the FedEx Cup title and a $10 million bonus with a victory at the Tour Championship.
Phil Mickelson would be 15th in the standings, and Woods would be 24th.
The fourth and final U.S. Ryder Cup pick for captain Jim Furyk, scheduled for Monday morning, will not be made until after the BMW Championship concludes.