#1 Seth Rollins
This is probably the most likely match for Brock Lesnar at the Saudi Arabia show. Lesnar was beaten in no time by Seth Rollins at WrestleMania 35, losing the Universal title to the Beastslayer.
Rollins has spoken about how he would be interested in a rematch with The Beast sometime down the road: "I’d be up to the task… I would definitely be open to giving him a rematch even though I do know what’s at stake if he were to beat me," said Rollins in an interview with Express Sport.
While I don't see this feud lasting a long time, a match-up between the two, and a victory for Rollins, could finally put an end to the feud with Lesnar's rematch granted.
Rollins will retain the Universal title, and perhaps his next challenger leading up to Survivor Series, will be revealed at the Saudi Arabia show.