Washington coach Steve Sarkisian made the announcement on Tuesday in a statement, but did not specify what Middleton did. The school said there would be no further comment.
Middleton was a prized recruit who arrived at Washington in 2008. He played in all 12 games his freshman season, one of 12 true freshman to play for the Huskies in their 0-12 season.
Last year, Middleton started 11 of 12 games in Sarkisian's first season. Middleton had 26 catches for 257 yards and three touchdowns.
During spring practice Middleton was passed by backup Chris Izbicki on the depth chart, but was expected to be a key part of the Huskies offense this fall.