Ford underwent an MRI on Saturday, a day after leaving Oakland's 31-27 preseason loss to the Arizona Cardinals in the first quarter.
Ford missed six games last season for the Raiders with a sprained left foot, although coach Dennis Allen said this one doesn't appear as serious.
"Obviously, it looks like Jacoby is going to miss a little bit of time, don't know exactly to what extent yet," Allen said. "We're still seeing where he's at."
Allen couldn't rule out the chance that Ford would miss the opener on Sept. 10 against San Diego.
The Raiders have only three receivers on the roster who ever have caught a pass in the NFL and all are nursing injuries. Darrius Heyward-Bey left the game Friday with a sprained shoulder that isn't believed to be serious. Denarius Moore hasn't played in the preseason as he recovers from a hamstring injury originally sustained during minicamp in June.
Allen said Moore is getting closer to returning, but the team might need to look outside the organization for help at receiver.
Ford and Heyward-Bey weren't the only players to leave Friday night's game with an injury as Oakland dropped its second straight preseason game.
Backup quarterback Matt Leinart got stitches in his right index finger after being knocked out by an illegal hit by Ricky Lumpkin in the second half, and backup running Mike Goodson had weakness in his shoulder in his first game since being taken to the hospital with a neck injury earlier in training camp. Neither of those injuries appear to be serious.