Melendez, the former Strikeforce titleholder and ESPN.com's top-ranked contender among lightweights, will make his second appearance inside the Octagon. In his UFC debut on April 20, Melendez (21-3) was on the short end of a split decision to promotion champion Benson Henderson.
In his most recent outing on March 3, Sanchez defeated Takanori Gomi by split decision. The win lifted Sanchez's professional record to 24-5.
After an impressive run as Bellator's 185-pound champion, Lombard (32-4-1) relinquished his title to sign a multifight deal with UFC in April 2012. But he has struggled with his new promotion, winning just one of three fights.
Marquardt (32-12-2) has dropped two consecutive fights.
UFC officials also announced that negotiations are ongoing to hold a heavyweight title fight between champion Cain Velasquez and former titleholder Junior dos Santos as the card's main event. If an agreement is reached, the fight will be the third title showdown between Velasquez and dos Santos in fewer than two years.