Sunday's game against the Chargers remains scheduled for 1:25 p.m.at the Oakland-Alameda County Coliseum.
According to the San Francisco Chronicle, receiver Michael Crabtree and other Raiders players wore masks while practicing Thursday.
The NFL is keeping an eye on the wildfires in Northern California and has been exploring options to move Sunday's game between the Oakland Raiders and Los Angeles Chargers if it becomes necessary.
As of Friday morning, Lockhart said, the game remained scheduled to be played in Oakland. He acknowledged the National Football League has looked at possible backup sites for the game but would not specify where, saying only he "would expect it to be an National Football League stadium".
Officials in San Diego, the former home of the Chargers before they moved to Los Angeles for this season, reportedly would be receptive to hosting the game if it can not be played in Oakland.