Aaron McKenna is preparing to face a new opponent on Saturday night for his first defence of his WBC International Middleweight title after the Monaghan boxer's original opponent Linus Udofia withdrew, citing illness as the reason.It means McKenna, who has an unblemished 17-0 record, will face Mickey Ellison in Liverpool on the undercard of the fight between Natasha Jonas and Mikaela Mayer.McKenna will be the favourite against the 33-year-old Ellison who has a record of 14-6, but speaking at a Sky Sports press conference, the 24-year-old did not hide his frustration with Udofia's decision to pull out on fight week."It's very frustrating for me because it's a regular occurence at this stage," he said."Last year when Shakiel Thompson pulled out so close to the fight, he bottled it and then Liam Williams was offered two fight dates and he went to Mexico instead and he turned them down."And now this one, which was really close to the fight date just yesterday."McKenna, who has enjoyed eight knockout victories thus far in his career, was taken the distance in his last outing in June against Uisma Lima, albeit winning the York Hall contest comfortably by unanimous decision.McKenna is currently ranked 25th on the most recent WBC world rankings.