Chelsea, boosted by the signings of Spain duo Cesc Fabregas and Diego Costa, are the early favourites for the Barclays Premier League after winning their opening three games.
Costa, a £32million buy from Atletico Madrid, has been an instant hit with four goals in three games while former Arsenal midfielder Fabregas, £30million from Barcelona, has also shone.
Zola said: "I think it was very clever the way they used their money
They have a strong team, in every position they are very good.
"The quality of the football has been made better and I believe that Fabregas has a lot to do with that.
"Chelsea look like they will be one of the teams to beat - but the Premier League is long and the tough moments will come."
Zola was speaking at the Soccerex Global Convention in Manchester where he was part of a panel discussing the summer's transfer business around Europe.
Statistics produced by marketing firm Prime Time Sport to accompany the talk underlined the spending power of the Premier League.
For the first time, combined spending by English clubs topped the one billion euros mark (£800.5million).
Of those, Manchester United spent the heaviest, with their £157million new signings including club record £59.7million transfer Angel di Maria.
Zola believes United had to play catch-up but is unsure whether it will pay off.
The Italian, 48, said: "Only time will tell
Obviously the intentions are good, they know the competition in this country is big.
"They wanted to make sure they had the quality in the squad to face the challenge.
"Manchester United want to make sure they are competitive in the next few years.
"The potential is there but football can be affected by many things
I hope for Manchester it will go well."
Yet while United's transfer spending may be eye-popping, Prime Time's figures also reveal that the club - despite the departures of Danny Welbeck and Tom Cleverley - still boast the highest number of homegrown players in the Premier League with seven.
Arsenal and Aston Villa both have six, Liverpool and Newcastle five while QPR, Hull and Sunderland have none.
United's seven are Ben Amos, Jonny Evans, Tyler Blackett, Rafael, Darren Fletcher, Jesse Lingard and Adnan Januzaj.
Former United assistant boss Mike Phelan has said he feels the club have lost some of their identity with the £16million sale of academy graduate Welbeck to Arsenal.
But Zola hopes manager Louis van Gaal will still give opportunities to those who have come through the system.
He said: "Van Gaal is the type of manager if he has a good young player, he will play him.
"He is known for that
The young players will have to raise their standards but the quality of the players they have bought is high."
Another player to have moved in the recent transfer window is Zola's former protege Mario Balotelli.
Balotelli, the controversial striker who played under Zola for Italy Under-21s, joined Liverpool from AC Milan for £16million.
Zola said: "I believe Mario technically and tactically is the perfect fit for Liverpool.
"I think it will depend a lot on Mario's attitude towards it.
"I think it is very important for him
I believe it is a massive opportunity for him to make a step forward in his career and his knowledge of football.
"I hope Mario takes the chance very well and Liverpool can have a lot of benefit from it."
Source : PA
Source: PA