The event will be held at Mandalay Bay Events Center in Las Vegas. A victory by Maynard puts him back in the conversation for a title shot.
This bout marks the second time these two have met inside the Octagon. In their first meeting, on Jan. 11, 2010, Maynard defeated Diaz by split decision.
Maynard, who came up short in two attempts to lift the 155-pound belt from ex-champion Frankie Edgar, suffered a first-round TKO loss to TJ Grant during a title eliminator on May 25. The loss dropped Maynard to 1-2-1 in his four most recent outings.
Despite his current woes, Maynard (11-2-1) remains among the top-rated lightweights in mixed martial arts. He is ranked sixth by ESPN.com, while UFC.com has him at No. 4.
Diaz suffered the first knockout loss of his career on April 20, when Josh Thomson finished him in the second round. The loss was his second in a row.
Diaz faced Benson Henderson in December 2012 for the lightweight title, but came out on the wrong end of a unanimous decision. Diaz will take a professional record of 16-9 into his bout with Maynard.