But he insists his reasons for travelling to the other side of the world to defend his world title in the toughest test of his career was not driven by the pay pot on offer.
And he points to the finer details of his training camp to prove it.
McDonnell footed the bill for a four-strong team, plus his wife and daughter, to accompany him in Dubai for the final fortnight of the camp.
And that team will be by his side in Japan this week ahead of his clash with pound-for-pound ace Naoya Inoue on Friday.
The ferocious Inoue is the hot favourite but McDonnell is supremely confident of victory – and says the finances prove it.
“If I didn’t think that I was going to beat Inoue, I wouldn’t have been going to Dubai and spending a load of money,” he told The Star.
“It’s cost me an absolute fortune to take them all out.
“I had to fly them all out and put them up for a fortnight. I’ve had to foot all of the bill.
“If I didn’t believe I could win I would have just flown straight to Japan on fight week, gone in there and collected my money.
“But I do believe I can win.
“This is an investment.
“It’s cost me a fortune but it’s going to be worth it.
“I’ll go in there and get a massive win.”