Haye, 35, fights Mark de Mori in the first step to a possible fight with Anthony Joshua and McGuigan has been working on bulking up the former cruiserweight seen training began for the O2 Arena clash.
McGuigan was drafted in by Haye on the back of success with Carl Frampton and the son of famous fighter Barry is confident his work will bear fruit with a victory over 33 year-old de Mori this weekend.
“I’m really excited about David’s comeback,” said McGuigan.
“We’ve been talking about it for a full year so it’s not been rushed and been done properly.
“He’s here and he’s firing on all cylinders. Everyone who has seen him on the pads has been blown away. He’s bigger and has the same speed, so you’re all going to be shocked when you see him on Saturday night.”
On the challenge in front of Haye, McGuigan added: “Mark de Mori hasn’t got that much amateur experience, but he’s rugged and raw, so he’ll prove to be a test on Saturday night.
“He’s never been in with a world class heavyweight though so it’s make or break for him.”
Haye v de Mori is live on Freeview channel Dave at 9pm on Saturday night. For tickets visit axis.com.