Dempsey, 33, had a procedure to address the issue, according to Seattle general manager Garth Lagerway.
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The Sounders say that Dempsey could return this season, but stressed that he has not yet been cleared to play.
Seattle is six points back of Portland for the West’s final playoff spot, but has played two less games than the Timbers.
Dempsey has 8 goals and 2 assists in 17 games for Seattle this season.