Harry Kewell's agent, Bernie Mandic on BBC 5 Live's Sportsweek's programme:
"Harry wanted to go to club he felt were on the up.
"Manchester United had a huge amount of success over the years. Liverpool have started to splutter and drop off since 1990. I think United are destined to go into a downturn."
Kewell will make his debut in a friendly in Cologne on Wednesday.
But he could have been earning "30% more" according to Mandic.
"I think United, if you look at cycles, are destined to go into a downturn whether this year, next year, whenever."
Mandic dismissed the notion that Kewell may not have held down a regular place in the United side.
He said: "I think Harry, considering the money being offered, would have been guaranteed a first team place. You don't pay that sort of money to an individual or a club to sit on the bench. That wasn't an issue."
The agent continued to defend his part in the deal that leaves Leeds with only £3million of the £5million fee.
He said: "I'm proud of the deal I did, I'm only concerned about the player. If he is happy to take a deal that is 30% lower at Liverpool than is being offered elsewhere, then I have to accept that.
"If it costs me and a company money, so be it. Obviously I would have been on a far better return from a bonus perspective if the company received £4million rather than £2millon but I have to be guided by my client.
"We had a £9million bid two days before the deal with Liverpool was done. That would have meant my company getting £4million. The bonus was on a sliding scale and had been agreed by Leeds.
"They had clubs lined up for Harry. It was put to us that if Harry wanted to leave with his head high and considered a Leeds legend, he had to accept their deal.
"The bids came from Chelsea and Manchester United among others."