Washington coach Randy Wittman made the announcement before Monday night's game against Chicago.
Blatche was injured in Saturday's win in Charlotte. After an MRI exam, he was advised to stay off his feet.
Blatche missed three games earlier this month with a sprained right shoulder. He was averaging 10 points and seven rebounds per game.
Since Wittman became coach last week, Blatche had been coming off the bench. To help replace him, Washington recalled center Hamady Ndiaye from Iowa of the D-League.