Dukes had been expected to be the Nationals' starting right fielder but he was hitting .143 (3-for-20) this spring. He hit .250 with eight home runs and 58 runs batted in over 107 games for Washington last season.
Nationals Manager Jim Riggleman told The Washington Post the move was a baseball decision and, "We like some of our other options in right field, really."
The Post said Riggleman may go with a platoon system utilizing some combination of Roger Bernadina, Willie Harris, Justin Maxwell and Mike Morris.
Dukes has been in the major leagues for three seasons, playing for Tampa Bay before joining the Nationals. He has a career batting average of .242 with 31 home runs and 123 RBI in 240 games.
Also Wednesday, Washington released right-handed pitcher Logan Kensing. Last season Kensing was 1-1 with an 8.69 earned run average in 26 appearances.