US PGA Tour officials were skeptical of completing a full 72 holes in the BMW Championship after heavy rain wiped out all play Sunday, swamping Aronimink Golf Club.
More than three inches of rain since late Thursday night drenched the layout and organizers decided Sunday afternoon to delay the final round until 7 a.m. Monday (1100 GMT) with threesomes starting off the front and back nines.
"We will do everything we can to play tomorrow but we'll just see what Mother Nature gives us," PGA competitions vice president Carlton "Slugger" White said.
"We just have to wait until in the morning to see exactly what we're going to have to try to do."
Britain's Justin Rose owns the 54-hole lead on 17-under par 193, one stroke ahead of Northern Ireland's Rory McIlroy and American Xander Schauffele. The Englishman could become the world number one with a victory, even if the event were declared complete after three rounds.
There was also the prospect of a Tuesday finish because of the showers that have soaked the course.
"It's like we are kind of having to shovel sand against the tide, unfortunately, and that's the sad part," White said.
"The fairways are iffy and the tee boxes sloshy. The greens are fine. The bunkers were OK. We just have a golf course that we just couldn't play.
"We can't push water around and we've gotten over three inches of rain since last night and today."
Schauffele was considered a top contender to be US Ryder Cup leader Jim Furyk's captain's choice final pick. That announcement was set for 9 a.m. Monday but that was uncertain due to the final-round postponement.
The top-30 spots in the US PGA season FedEx Cup standings were also to be decided in the final round, with only 30 players set to qualify for the Tour Championship in two weeks at Atlanta.
A bizarre scenario faces three-time major winner Jordan Spieth should a rainy forecast prove true and no golf takes place on Monday.
The American shares 27th after 54 holes and is projected to fall from 27th to 31st in the points standings, one place shy of Atlanta. Spieth also must qualify for the season finale to play the minimum 25 events this season or face a fine.
Two other events have finished beyond the weekend, including Australia's Jason Day and Swede Alex Noren in a Monday playoff at Torrey Pines and American Troy Merritt winning July's Barbasol Championship in Kentucky on a Monday.