ARLINGTON, Texas -- Texas Rangers manager Ron Washington has unexpectedly resigned, saying he needs to devote his full attention to an "off-the-field personal matter."

The stunning announcement Friday came one day after the Rangers lost their sixth straight game and became the first team mathematically eliminated from playoff contention. Only three years ago, Texas reached its second consecutive World Series under Washington.

Washington said in a statement that his resignation had nothing to do with the disappointing season. The statement did not disclose any details of why he was leaving.

General manager Jon Daniels says the manager had given the team permission to acknowledge that the move "was not drug-related."

During spring training in 2010, it was disclosed that Washington had admitted to using cocaine once the previous year.