#1. Matt Riddle
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Matt Riddle is blunt in who he wants to call out and who he wants to talk trash to. Two such names that he's brought up on many occasions are Goldberg and Brock Lesnar. There were rumors that he had a verbal altercation with Brock Lesnar, but a documented interaction was one behind-the-scenes with Goldberg.
It seemed as candid and tense as one would imagine, with Goldberg telling Matt Riddle to stop calling him "bro". Either way, he didn't seem very appreciative of Riddle bringing up his name as many times as he has.
It could be real, or Goldberg is simply smart enough to capitalize on it along with Riddle. While The King of Bros could be in NXT for a while, his jump to RAW or SmackDown is inevitable and when that does happen, there could still be a possibility of seeing Riddle vs Goldberg.
It all depends on how WWE views Riddle, but if they do see him as the potential main event star that he is, then he's the best option to retire Goldberg.