According to SI.com’s Justin Barrasso, the Beast Incarnate’s advocate Paul Heyman is pushing behind the scenes to have Samoa Joe win the WWE Universal Title at SummerSlam.
Here is an excerpt from the SI.com article:

SI.com has learned that Lesnar’s return to the UFC is imminent, and he will fight Jon Jones as well as fulfill his WWE obligations at the Royal Rumble and WrestleMania 34. This all affects the upcoming SummerSlam, as the likelihood that Lesnar keeps the WWE Universal Championship, or takes any punishing moves, is all but dimmed, which is another reason he will be hidden in this Fatal 4-Way with Braun Strowman, Roman Reigns, and Samoa Joe.

It should be noted that Lesnar is being advertised for WWE events after SummerSlam including the September 24th No Mercy PPV in Los Angeles, CA.
Lesnar will still need to re-enter USADA’s drug testing pool before he competes again. Both Lesnar and UFC light heavyweight champion Jon Jones has been campaigning to fight each other at heavyweight when Lesnar’s suspension is up.