Sam Cassell is leaving Washington to join the Clippers and Doc Rivers . (Katherine Frey/The Washington Post)

Sam Cassell is leaving the Washington Wizards after five seasons to take an assistant coaching position with the Los Angeles Clippers, people with knowledge of the situation confirmed Saturday.

Cassell joined the Wizards as a member of Flip Saunders’s staff in 2009, one year after winning his third championship in Boston with Doc Rivers, the current president and coach of the Clippers.

A reunion with Rivers has been rumored for several weeks, with the Clippers losing assistants Tyronn Lue (to Cleveland) and Alvin Gentry (to Golden State) this offseason. According to people familiar with the situation, Cassell will receive a huge boost in pay but Washington was reluctant to let him leave for what was perceived as a lateral move. A call from Rivers helped convince the organization to let Cassell free. An official announcement is expected next week.

Cassell, a native of Baltimore, had a successful 15-year playing career with Houston, Phoenix, Dallas, New Jersey, Milwaukee, Minnesota, Clippers, Boston, earning one all-star appearance in 2004. In nearly three seasons with the Clippers, Cassell averaged 14.6 points, 3.2 rebounds, and 5.4 assists and led the franchise to the Western Conference semifinals in 2006.He got his initial taste of coaching in his final season with the Celtics and has been a valued member of the staff in Washington.

John Wall and Bradley Beal both credited Cassell with helping them develop as players. Wall emerged as an all-star last season. This offseason, Cassell provided another significant contribution by helping to lure likely Hall of Famer Paul Pierce to the Wizards with a strong recruitment pitch.

Cassell is the second assistant to move on this summer, with Ryan Saunders leaving to join his father, Flip, in Minnesota. The Wizards replaced him with former Maryland women’s assistant and longtime high school coach and trainer David Adkins.