Manuwa (15-2) has yet to fight this year as he has been recovering from an injury. In his last appearance, he was knocked out by top contender Anthony Johnson.
Saint Preux (19-8) stepped in on short notice and fought Jon Jones for the interim UFC light heavyweight title in April, losing via decision. He has recovered from a broken arm suffered early in that fight.
Struve (27-8) knocked out Antonio Silva in 16 seconds this past May, while Magomedov (14-1) is on a nine-fight win streak.
UFC 204 takes place October 8 from England and is expected to feature Michael Bisping defending his middleweight belt vs. Dan Henderson.