Duncan played in just 11 games with New York last season but slugged 30 home runs with Triple-A Scranton/Wilkes-Barre en route to being named the Most Valuable Player of the International League.
The 6-foot-5 slugger appeared in 68 games with New York in the past three seasons, batting .219 with eight home runs and 24 RBIs.
Duncan has fared much better in the Minors, including in 2009 when he led the International League with 30 home runs and 99 RBIs and also batted .277 with a .370 on-base percentage.
In nine Minor League seasons, Duncan is a career .258 hitter with 170 home runs, 523 runs scored and 599 RBIs in 905 games.
Duncan is also the son of Cardinals pitching coach Dave Duncan and the brother of free-agent outfielder Chris Duncan.
Rhett Bollinger is a reporter for MLB.com.
This story was not subject to the approval of Major League Baseball or its clubs.