"The drama surrounding the Lions' running back position has thickened.

First, the trade for Eagles running back Ronnie Brown was nixed Wednesday when Jerome Harrison failed his physical in Philadelphia. Harrison was not at the Lions' practice Thursday morning.

Neither the Lions nor Harrison's agent, Mitch Frankel, responded to questions regarding Harrison's health.

Secondly, according to a report from CBSsports.com's Mike Freeman, "Lions running back Jahvid Best has been advised by people close to him to 'strongly consider sitting out the year' after suffering his second concussion of the season last Sunday."

The family is fearful, according the report, that another concussion this season would jeopardize his career."