Oakland headed into the opener of a three-game series at Seattle on Monday night with the worst record in the American League at 54-71 following three straight years in the playoffs.
The 63-year-old Washington spent 11 seasons as an A's coach before becoming manager of the Rangers in 2007 and leading Texas to a pair of AL pennants in 2010 and 2011. Washington rejoined Oakland as a coach in May to work with infielders.
"Any time you are a part of a major league dugout it means to me you really have an opportunity to make a difference," Washington said by text message. "That is what I want to do, make a difference."
He has specialized in working with infielders on their defense. His challenge this season has been helping shortstop Marcus Semien, who has 31 errors.
Washington was instrumental in developing the infielders during his first A's stint. Oakland led the league in fielding in 2004 and 2005 and was second in 2006.
He resigned as Rangers manager Sept. 5, saying he needed to devote his full attention to an "off-the-field personal matter." He later acknowledged he had broken wife Gerry's trust.
Washington had hoped to get back into baseball -- and then the A's came calling when they needed help with their struggling defense.
Washington, who played parts of 10 seasons in the majors as an infielder for five teams, was popular with the Oakland players and a key in the development of retired six-time Gold Glove third baseman Eric Chavez -- not to mention Mark Ellis, Miguel Tejada and Jason Giambi.
Chavez presented his third Gold Glove to Washington, who began coaching in the New York Mets organization in 1991 and later managed their Class-A club.
Gallego was in his seventh season as third-base coach and 19th overall season with the Oakland organization, including 12 years as a player.
Also Monday, the A's placed right-hander Kendall Graveman on the 15-day disabled list with a strained left oblique muscle and recalled infielder Max Muncy from Triple-A Nashville.
Ron Washington hired as A's third-base coach
Pedro Gomez discusses the Oakland Athletics' hiring of Ron Washington, who resigned as Rangers manager in September, as their third-base coach.