A left hamstring injury in spring training has kept Wang out all season. He is expected to pitch out of the bullpen.
The right-hander went 5-4 with a 4.04 ERA last season after needing almost two years to come back from shoulder surgery.
Wang has started 115 of his 120 games in five seasons with the Yankees and last season with Washington, going 59-29 with a 4.15 ERA. He has a 2.70 ERA with one save in five career relief appearances.
To make room for Wang, the Nationals placed right-hander Ryan Mattheus on the 15-day DL retroactive to May 21 with a strained left foot.