Storen, 25, allowed three earned runs over ⅔ inning Friday against the Mets in the latest of a series of bad performances this season. The struggling reliever has a 5.95 ERA on the season and has looked out of sorts for months.
Nationals Manager Davey Johnson told reporters, "He need[s] to get right mentally and mechanically because I need him. It's that simple."
Storen had been the closer for Washington and saved 42 games for the team in 2011. He missed the first 89 games of the 2012 season after having surgery to remove a bone chip in his elbow. Storen would eventually share closing duties with Tyler Clippard, who had taken the role on an interim basis in Storen's absence.
The Nationals made the 2012 postseason, but in Game 5 of the NLDS Storen blew the save while protecting a 7-5 lead against the Cardinals. That meltdown helped prompt Washington to sign Rafael Soriano in the offseason to become the team's new closer.
Following Storen's demotion, Clippard, who is good friends with Storen, had strong words for the organization. Clippard told reporters, "I think this had been handled very poorly by the organization."
Storen leads Nationals' pitchers with 47 appearances on the season.