Zimmermann, who is entering free agency this offseason, wrote that it was difficult to put his appreciation for his fans into words.
“Although I may no longer wear the curly W on my head or chest, Nationals fans always will be in my heart. Thank you again for everything!” Zimmermann said through his agent, Mark Pieper.
Pieper did not rule out a return to Washington for his client.
The right-hander spent his entire career with the Nationals since signing with them in 2007. Zimmermann, 29, has 70 games and has been named to the All-Star team twice.
Zimmermann finished this season 13-10 with a 3.66 ERA.
Washington finished the year 83-79, missing the postseason and finishing second in the NL East behind the Mets.
- Beth Maiman