Henderson was at practice on Wednesday. He has played in only two games for Minnesota this season, primarily on special teams.
Henderson declined to specify the substance he was punished for, but says he "didn't do anything wrong" and blames the positive test on a prescription product he took in training camp to remedy allergic reactions.
Henderson appealed his punishment with the league in September, but it was denied.
He understands the zero-tolerance policy, but believes the NFL should reconsider some of the rules.
Copyright 2010 by The Associated Press