There's no official word on the match but Black's opponent as of earlier this afternoon was planned to be Cesaro. Black is currently on the SmackDown roster while Cesaro is a RAW Superstar.
Black has appeared in cryptic backstage vignettes since being assigned to the blue brand in the 2019 Superstar Shakeup, but he has not had his in-ring TV return. Black's vignettes have had him begging for another Superstar to come pick a fight, and it looks like Cesaro may be the one to answer that challenge.
It will be interesting to see if the Black vs. Cesaro feud kicks off on tonight's SmackDown episode as the Road to Extreme Rules heats up.