According to ESPN's Adam Schefter, McFadden's injury occurred on his first carry of the game, but he tried to play through the sprain before aggravating it again in the second quarter.
Schefter's postgame report also said that the McFadden's sprain is of the high ankle variety, meaning he'll have the dreaded "week-to-week" prognosis hanging above his head. McFadden is currently scheduled for an MRI Monday so the results should be revealed shortly.
As for Goodson, the fourth-year running back turned his ankle in the third quarter after replacing McFadden. Vic Tafur of the San Francisco Chronicle reported after the game that team doctors felt Goodson didn't need X-rays so his injury is probably just a pain tolerance issue at this point.
With two ball carriers going down, the Raiders essentially abandoned the run with fullback Marcel Reece filling in in pass protection. Third-string running back Taiwan Jones got his first carry of the year due to all the injuries, but managed only two yards on it.
It's unclear at this point who will start for Oakland if McFadden and Goodson can't go against the Baltimore Ravens next week. Reece doesn't seem like a terrible option though, after he compiled a game-high 95 receiving yards while also chipping in a touchdown. Reece averaged 6.6 yards a carry on the 17 attempts the Raiders gave him in 2011.