(Detroit, MI)  --  The injury-riddled Vikings secondary will have its work cut out when they play at Detroit this afternoon.   The Lions have one of the top receivers in all of pro football in Calvin Johnson and a hard-throwing quarterback in Matthew Stafford.  Head coach Leslie Frazier knows his defensive backfield has struggled this season and he says they will do a few new things to help them defend better.  The Vikings will announce later this morning whether Christian Ponder and Adrian Peterson will play.  Kickoff is set for noon.