The Colchester man was originally due to face Carson Jones on the Wembley bill, but the American was forced to pull out through illness.
"We're disappointed to hear the news late last night that Carson Jones was unable to make the flight to the UK due to illness," Boxing Scene quotes Hearn as saying.
"We worked tirelessly last night and were delighted to secure Rivera, who was approved by the IBF as a suitable contender.
"Both have explosive styles and we're expecting a great fight on Saturday."
Purdy and Jones were supposed to fight each other in December, but the former withdrew on that occasion.