Justin Rose could become world number one without hitting another shot
The first groups are scheduled to tee off at 7.30 a.m. local time (1130 GMT), with the final threesome out at 9.20.
But with more rain forecast at an already waterlogged course, there are no guarantee conditions will be playable.
Officials are leaving their options open, among them reducing the event to 54 holes.
Under tour rules, half the field must complete the final round by Monday for an event to extend into Tuesday.
If the tournament is cut to 54 holes, Rose would win after posting a 17-under-par 193 total on Saturday, one stroke better than Northern Irishman Rory McIlroy and American Xander Schauffele.
Schauffele bogeyed the 54th hole when he missed a 10-foot putt to fall out of a tie for the lead.
The BMW Championship is the third of four FedExCup playoff events on the PGA Tour.