According to the Star Tribune, Henderson was unhappy that the Vikings did not come to a long-term agreement with Henderson last offseason, and consequently, Henderson could take comparable money from another team this offseason.
Henderson appeared in 14 games for Minnesota during the 2012 regular season, recording a career-high 79 tackles and there sacks. Henderson also forced a fumble.
Minnesota linebackers Jasper Brinkley and Marvin Mitchell are also unrestricted free agents. The Star Tribune concludes that Brinkley is more likely to return than Henderson -- if Brinkley feels "comfortable" that the Vikings indeed believe that he is Minnesota's long-term middle linebacker.
Brinkley, who will turn 28 in July, recorded a career-high 97 tackles in 2012, appearing in all 16 regular season games for the Vikings.