Best also missed time during this preseason because of a concussion.
"He has a protocol to go through and we'll see where he is with it," Schwartz said Monday.
Best ran for 37 yards on 12 carries in Detroit's 25-19 loss, but now his status is uncertain for next weekend's game against Atlanta. Best has 390 yards rushing this season. He also has 27 catches for 287 yards.
This is his second year as a pro. When he was a college player at California, Best missed a few games after a fall knocked him out and sent him to the hospital with a concussion and sore back.
Schwartz says Best was available throughout the game Sunday but started experiencing symptoms "pretty long after the game was over."
"That's not unusual," Schwartz said. "We've had some of those that they're not even on the radar until 10 o'clock the next morning and we'll have them show up on the injury report and show up here and say, 'Hey, I didn't sleep at all last night,' or, 'I'm feeling nauseous this morning', or, 'The light was driving me crazy when I came into work,' and they're all signs of concussion symptoms."
Copyright 2011 by The Associated Press