PONTIAC, Mich. -- Detroit Lions safety Tommy Bennett has been suspended for the final four games of the season for violating the NFL's policy banning steroid use.

Detroit coach Marty Mornhinweg said the violation stems from an injection into Bennett's hamstring, between the time he was released by the Arizona Cardinals on Aug. 16 and signed by the Lions on Aug. 29.

"Tommy did not know he was receiving a banned substance," Mornhinweg said.

Bennett, in his sixth season, had 26 tackles for the Lions this season.