Ed Woodward said Sir Alex Ferguson has been supported in every player he has wanted to buy and cited the signing of Robin van Persie as an example.
Woodward also said United's owners will not sell the club for "many, many years" despite ongoing interest and that the club's debt, partially reduced due to the IPO share sell-off in August, was easily handled by United's income.
He said: "Every single player Sir Alex Ferguson has wanted to buy he has been supported. Some have slipped through our fingers but we have never said that we cannot afford a player.
"Robin van Persie is a good example, one of the best players in the world and we easily had the financial capacity to do that.
"We have a pretty low level of leverage. Interest payments of £31million leaves a significant amount of money, around £76million and we decide what we do with that.
"We are very comfortable about the ability to fund the interest and there will be more income growth next year from the new Premier League media deal."
The sell-off of 10 per cent of the Glazers' shares in the club in the IPO sale raised some questions over the American family's long-term involvement, but Woodward said they had no interest in cashing in the rest of their holding.
He added: "There is always interest in this business. It is a phenomenal brand and club, but they are not willing sellers at all, they won't even engage, they are long-term investors.
"It's a very popular business that people have interest in. The answer is: 'not for sale'. I talk to them [the Glazers] every day and the excitement they have in this club is undiminished and I don't see them selling completely for many, many years."
Woodward did accept, however, that one of the Glazers could dispose of their shares at some point.
He added: "They could - they are a family of six siblings and from time to time, seven to 10 years, who knows if one wants to sell a small piece or not."
Woodward revealed that India and Australia are both on a shortlist of countries for United to tour in the summer.
The club are also to open an office on the east coast of the United States to cash in on growing interest in football in North America.