The Ring has learned that the middleweight contender will square off against Austin “Ammo” Williams in a fight DAZN will stream September 4 from Prudential Center in Newark, New Jersey.

Mielnicki (23-1, 13 KOs), of nearby Roseland, will box at the venue for the sixth time since he made his pro debut at the home arena of the NHL’s Devils as a 17-year-old high student in July 2019.

Mielnicki’s middleweight championship aspirations hinge on beating Williams, a southpaw who lost a unanimous decision to WBC 160-pound champ Carlos Adames in his last fight March 21 in Orlando, Florida.

The 24-year-old contender has won 15 straight fights since James Martin upset him by majority decision in an eight-rounder in April 2021. Mielnicki fought to a 10-round majority draw with unbeaten contender Connor Coyle (22-0, 10 KOs) in February 2025, but the result of their bout was changed to a no-contest because Northern Irishman tested positive for a performance-enhancing drug.

Mielnicki is ranked No. 2 by the WBO and No. 7 by the IBF and WBC.

Matchroom Boxing, the promotional company run by Eddie Hearn, announced it signed Mielnicki on Saturday. He was previously promoted by Sampson Boxing and Bob Arum’s Top Rank Inc. and fought on cards arranged by Al Haymon’s Premier Boxing Champions.

Williams (20-2, 13 KOs), a Milwaukee native who fights out of West Palm Beach, Florida, has lost only to Adames (25-1-1, 18 KOs) and WBO super middleweight champ Hamzah Sheeraz (23-0-1, 19 KOs). England’s Sheeraz stopped Williams in the 11th round of their June 2024 bout.

Williams, 30, is rated No. 11 by the WBO and WBC and No. 14 by the IBF.