Former belt holder Jessie Vargas shapes as the man most likely, after Pacquiao's withdrawal on Friday due to his commitments as a Philippines senator.
Horn's trainer Glenn Rushton said with the Australian's rise to world champion, he had become the hunted and would have no trouble luring a big-name fighter to Brisbane for a November title defence.
Rushton anticipates a new opponent being locked in within a week or so, with the venue dependent on the profile of Horn's rival.
"We want to bring a big fight to Brisbane this year," Rushton said on Friday.
