Spurs are the only Premier League club yet to make a summer signing, despite selling England defender Kyle Walker to City for a deal that could reach £50 million -- a record for an English player.

By contrast, the rest of last season's top seven clubs have all bought at least one player for £30m or more, while the capture of Benjamin Mendy took City's summer spending past the £200m mark.

Levy, who is notorious for extracting value from the transfer market, believes the spending will eventually 'catch up' with Tottenham's rivals.

"My view is that it's totally unsustainable. I'm not sure if that's the view of the other Premier League clubs, but certainly the prices that are being paid for other Premier League players I can't see it being sustainable in the long term," Levy said in a Q&A with the NASDAQ stock exchange in New York.

"I think I am a custodian of this football club. This club has been around since 1882 and when I leave it will be somebody else. I think we have a duty to manage the club appropriately. I don't think that long term for any club it's sustainable to spend more than you earn. You can have periods where you do but over the long term you can't.

"I think that some of the activity that's going on at the moment is just impossible to be sustainable. If somebody is spending £200m more than they're earning then eventually it catches up with you. You can't keep doing it.

"We've managed the club, we think, in a very appropriate way. We've invested a lot of money in physical facilities for long-term growth. So we've got one of the world's best training facilities. We've invested over £100m in that facility.

"We're now investing in the stadium. The stadium is fundamental because with that we get more fans and more income and that's the way to clearly have a more sustainable business."

Levy was in New York for Spurs' preseason tour of the United States, where they will play Roma at Red Bull Arena in the International Champions Cup on Tuesday.

Manager Mauricio Pochettino has included a number of young players -- including Tashan Oakley-Boothe, the first "millennium baby" to feature for Spurs after his debut against Paris Saint-Germain in Orlando on Saturday -- and Levy says the club will continue to prioritise youth development over new signings.

"The academy is important because we can produce our own players. We don't have to go and spend £20m, £30m, £40m on a player and obviously that homegrown player has an affinity with the club that a player we buy doesn't," he said.

"That's what the fans want to see. They want to have that passion. That's what you get with a homegrown player and that's why people love Harry Kane and sing that he's one of our own."

Tottenham's new state-of-the-art 61,500-capacity stadium, due to be ready for the start of the 2018-19 season, has rocketed to £800m but Levy insisted the cost of the project is not hamstringing the club in the transfer market.

"Regardless of the stadium project, today our position on transfers is that we have a coach that very much believes in the academy," he said.

"Unless we can find a player who would make a difference he would rather give one of our academy players a chance so that's regardless of the financing of the stadium.

"Obviously when you're building a stadium of this magnitude in a UK context it all has to be privately financed. There's no state help whatsoever.

"It is a challenge and we have to find the right balance but it's not impacting us at the moment on transfer activity because we're not yet in a place where we've found the player who we definitely want to buy but can't afford to buy."

Despite being unable to compete with their rivals in the transfer market, Levy believes Spurs' policy of frequently rewarding players with new contracts is a big selling point for the club.

"You just have to find the balance and the philosophy at Tottenham is that if a player does well we will reward them and we will keep rewarding them.

"That's one of the attractions of Tottenham that you may sign a five-year deal, but if someone does exceptionally well after a year we'll tear up that contract and give them another one."