ALLEN PARK -- Jahvid Best is back on the sidelines with concussion problems for the third time in the last two years, including once as a junior in college and earlier this year during Detroit Lions training camp.

The second-year running back didn't play in the final 10 minutes of Detroit's 25-19 loss to San Francisco but according to Lions coach Jim Schwartz, the concussion symptoms weren't evident until "pretty long after the game was over."

Best's final play came on first-and-15 from Detroit's 44-yard line. He took a handoff and tried going over the left side of the line, but the 49ers defense got too much penetration and took him down for a 1-yard loss.

It's not evident if the injury came when he was brought down on the rushing attempt. He spun into the arms of linebacker NaVorro Bowman, but the tackle was garden variety - nothing that would appear to be

"We'll see where he is," Schwartz said. "After the game, he started experiencing some concussion-like symptoms. We started getting him tested out. We never lost his availability during the game, even though we were using a little different package, trying to get more protection and had Maurice Morris in there to try and help chip and do some things like that, and trying to -- I don't want to say de-emphasize -- but it wasn't as important running the route as it was either running the ball or doing those things."

Morris finished the game with five carries for 20 yards and one catch for 8 yards. Best carried the ball 12 times for 37 yards and made six catches 73 yards, including a 32-yarder.

Still, Schwartz maintained he wasn't concerned about losing Best's ability to catch the ball out of the backfield.

"He's been effective in the pass game," he explained, "but Mo's also been effective in the pass game. We're working a lot of different combinations and things like that. It really had nothing to do with anything other than that.

"We're sitting there, looking, saying, hey look, we can get Matt some more time - going a lot to Calvin down the field ... trying to push some of those balls down the field. They were playing a little bit different coverage -- rather than 2-Man, they were playing 3-Cloud -- all game decisions."

Detroit attempted just one more deep pass -- an incompletion to Titus Young with 15 seconds left in the game - after Best's final appearance.

Regardless of the reasoning, the 5-foot-10, 199-pounder's history with head injuries raises red flags. As with all concussions, players must go through a battery of tests before they can be cleared for physical contact, then cleared for practice and finally, cleared for contact.

"I don't know that it makes us more cautious, but there is a protocol to go through and we're going to make sure that we clear those hurdles before he's cleared to be back on the field," explained Schwartz. "There's a whole protocol we follow in those situations. I mean, it's a little bit of a concern with (it being his) second one (as a pro), but it doesn't change the process when it comes to him being cleared. He'll be cleared when his symptoms diminish and he gets cleared for practice."