REUTERS: Englishman Justin Rose could become world number one without hitting another shot following Sunday's washout at the BMW Championship in Pennsylvania.
Persistent rain on Sunday gave PGA Tour officials no choice but to postpone the final round at Aronimink in suburban Philadelphia until Monday.
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 is 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.
Rose needs to win to displace American Dustin Johnson and become the 22nd man to be world number one since the rankings began in 1986.
The BMW Championship is the third of four FedExCup playoff events on the PGA Tour.
(Reporting by Andrew Both in Cary, North Carolina, editing by Ed Osmond)