The show confirmed Tuesday on Twitter that Sunday's episode will feature a showdown between Knight and LaBelle, both 76.
"The Master Class we've ALL been waiting for!" the post reads. "Y'all gotta get dressed up in ya Sunday's best for this classic affair."
Knight, known as the "Empress of Soul," promoted the battle on Instagram.
"This weekend join Me and @mspattilabelle for a #verzuz to remember!!! #loveMsGladys," she wrote.
Sunday's episode will stream at 8 p.m. EDT on the Verzuz Instagram account and on Apple Music. The battle will take place at The Fillmore in Philadelphia, Pa.
Knight, LaBelle and Dionne Warwick collaborated on the 1991 single "Superwoman."
Verzuz is an online series created by music producers Timbaland and Swizz Beatz. In each episode, two music icons compare and perform their respective hits.
Previous episodes have featured Brandy and Monica and Babyface against Teddy. Brandy and Monica's episode drew 1.2 million concurrent viewers on Instagram Live.