ALLEN PARK — The Lions were 5-0 when they started the 2011 season with running back Jahvid Best. He suffered a concussion in that fifth game, hasn’t played since and the Lions have gone 9-19 since including the playoffs.

 “Probably the biggest mistake I made last year was counting on Jahvid Best to come back. It’s no knock on him, he did everything he could to get back,’’ Mayhew said. “Based on the information we were getting medically I felt very comfortable he was coming back. We did not have a real plan to replace him.

“All of the information we had and acting in real time was that he would be back. In the history of the NFL  I can’t — I’ve asked people — I can’t think of a single player with a head injury who was asymptomatic that wanted to play that wasn’t allowed to play,’’ Mayhew said. “I think he’s the first one ever.’’

 Best was never cleared this season.

 His return to the NFL is very much in the air.

 “I’m not inclined at all to think it’s going to work out, I’m not inclined at all to rely on his return at this point,’’ Mayhew said. “If that happens, that would be great but I’m not at all inclined to rely on that.’’