According to Dave Meltzer on the Sunday Night’s Main Event podcast, a match between Brock Lesnar and WWE Champion Bobby Lashley is currently not being planned for Summerslam. Lesnar is not currently under contract to WWE and as of last week, Vince McMahon himself had not been in contact with him. In addition, WWE may only bring Lesnar back when Roman Reigns is able to feud with him, though it is not clear when that would be the case.
There are some possibilities here. Check out what Lesnar could do: