Yaya Toure says Arsenal's unbeaten 2003/04 Premier League season will never be repeated again due to the strength of the current game.
Arsenal won the 2003/04 Premier League having gone the whole league season unbeaten, with the only other side to have avoided defeat in one campaign being Preston in 1888/89.
Toure, who had a trial with Arsenal in the summer preceding their historic season, believes that the standard of the current English game dictates that this feat will never again be repeated however, with clubs such as West Ham and Leicester challenging the elite this season.
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"The Premier League is always improving and you see how the big clubs invest in players for a lot of money and this sequence in football â the Invincibles â it will never happen again in the Premier League," Toure told the Guardian.
"All the teams are spending money, buying big players. Like West Ham, even Leicester, Stoke spending on players from Barcelona. You can understand how the Premier League is so competitive because all the players want to come to England and want to improve, and want to play well. It's difficult, the Premier League."
After a club-record 11 consecutive Premier League victories, Toure and Manchester City fell at the hands of West Ham on Saturday, but Toure feels that Manuel Pellegrini's men have little to worry about in terms of their form.
"Sometimes it is just about luck," Toure said. "We played well against West Ham but we were unlucky again â the same as against Juventus.
"What are we going to do? We have been shooting, I don't know how many times, and I missed chances too. I should have blown the hand of the keeper off but it's football."
"Definitely he (Sergio Aguero) will come back," he said. "It's just about one goal with Sergio. He was injured a few days ago and now he is back and it's not easy.
"It's only six games in, 32 to go and it's going to be tough. It's good for the league and the fans as well. I'm not worried. This season the league is going to be tough. We started well and we just lacked that little bit extra. We have been shooting and we missed that luck to change this situation. It's the little margins."