Qualifying for the United States Grand Prix could be moved to Sunday after organisers at the Circuit of the Americas pushed back the start of Saturday's free practice session.
FP3 was due to get underway at 10am local time (4pm BST), but officials have refused to admit spectators until midday in Austin as heavy rain continues to fall at the track.
In the build-up to the race weekend, there had been doubts about whether the race would go ahead at all, with the worst of tropical storm Patricia hitting landfall in neighbouring Mexico in recent days.
Circuit organisers tweeted: "For the safety of our fans and employees, today's opening has been delayed until noon. Further updates will be forthcoming."
Lewis Hamilton can seal a third world title, if he wins and his nearest rival, Sebastian Vettel, fails to finish second.
For the safety of our fans and employees, today's opening has been delayed until noon. Further updates will be forthcoming. #USGP #COTA
— COTA (@circuitamericas) October 24, 2015