Darvish currently plays for the Nippon Ham Fighters of the Pacific League in Japan and is considered a dominating pitcher. Entering Saturday's action, Darvish is 13-2 with a 1.44 ERA for Nippon. Prior to this year, Darvish had pitched in 100 games for the Nippon, going 58-22 with a 1.81 ERA.
"[The Nationals] would be foolish if [they] didn't look him," the source said.
In the United States, Darvish helped Japan win the World Baseball Classic in 2009.