Arsenal manager Arsene Wenger expects big-spending Manchester City and much-improved Aston Villa to turn the Premier League's established big four into a big six this season.
However, the Frenchman warned it will not be easy for City, like Spanish giants Real Madrid, to turn their newly-recruited group of superstars into a balanced team.
"City look like they have made some great signings and have a high-quality squad, but it can take teams three months or more to find the right balance and to click," Wenger, who lost striker Emmanuel Adebayor and defender Kolo Toure to Abu Dhabi-owned City last month," told reporters on Thursday.
"Don't forget that Real Madrid finished second last season and have already a very strong squad - they are not rising from 10th like City will have to. And history is on the side of Real Madrid as well.
"But I think City will be there and be strong and remember that Aston Villa were challenging for the title (last season) until they faded in the last 12 games.
"When I arrived, Newcastle were there, at the top, and then it was Leeds," he said. "So I think the top four is not something that is set forever."
Speaking at the launch of Arsenal's charity partnership with the world-famous Great Ormond Street children's hospital, Wenger maintained he was confident that his team would again challenge for all the major honours.
He also had a slight dig at Arsenal fans who have become restless at a lack of silverware.
Asked what would be an acceptable level of success for the season, he said: "To win the league championship and to win the Champions League - anything else is a disaster - according to our fans!"
Wenger said his team were over-criticised last season for failing to win a trophy and only reaching the semi-finals of the FA Cup and the Champions League, losing to Chelsea and Manchester United respectively.
"I do not think it was a disastrous season," said Wenger whose side finished fourth in the Premier League and will find out on Friday who they must face to qualify for the Champions League group stage. "We had a long unbeaten run, we played our football and we had no blips."
Asked about a comment by Manchester United manager Alex Ferguson in which he did not mention Arsenal when talking of title rivals, he said: "Football is not as predictable or scientific as some people think and sometimes people are wrong in what they say."
Wenger is interested in adding one defender and one forward to his squad, at the right price, before the transfer window closes at the end of August.
"Don't forget that most of the business is done between August 26 and 31, at midnight," he said.
Asked if Arsenal were close to completing a deal to re-sign 33-year-old midfielder Patrick Vieira wenger said: "Not at the moment, no."