Bellator 300 was to be headlined by an unprecedented four championship bouts. Now it's down to three.
The fight was to be a rematch of a 2017 TKO win by Bader, who at the time was defending the light heavyweight title.
Vassell (23-8-1) was to enter this title challenge on a hot streak, having won five in a row at heavyweight, including four by knockout.
Bader (31-7, 1 NC) will not get a new opponent. He last fought in February, when he knocked out Fedor Emelianenko in his fourth defense of the heavyweight belt he won in 2019.
Bellator 300 will proceed with three title bouts: Lightweight champ Usman Nurmagomedov defends against Brent Primus in the main event, Cris Cyborg takes on women's featherweight challenger Cat Zingano in the co-main event, and Liz Carmouche puts the women's flyweight title on the line against former champ Ilima-Lei Macfarlane.