Play at the ATP $100,000 challenger in Fairfield, California, is being disrupted by the fires in the region.
Smoky conditions forced the suspension of matches on Wednesday, affecting most of the schedule.
There have also been evacuations in the area, affecting some players staying in local housing.
The event is being played at the Solano Community College, which is also an evacuation center for the area. Fires have now spread to the Fairfield region.
A full schedule has been announced for Thursday, but officials will first assess air quality at 9:30 a.m. local time, according to the tournament website. Should a move be required, as seems likely, UC Davis has been selected as the location.