Doolittle, who has 22 saves and a 1.45 ERA, was named a starter for the All-Star Game, which will be played at Nationals Park next Tuesday.
He told reporters Tuesday that he is giving up his spot on the All-Star roster but will participate in all the activities around the event except the game.
The move to the disabled list is retroactive to July 7, which means Doolittle will be ready to come back after the All-Star break.
Doolittle suffered the injury when he tripped on the mound recently and caught his toe, manager Davey Martinez said. He underwent an MRI over the weekend.
Kelvin Herrera will close for the Nationals while Doolittle is out.
The Nationals also optioned right-handed reliever Jefry Rodriguez to Triple-A Syracuse and recalled right-handed pitchers Wander Suero and Austin Voth.