After Chelsea won the league last season their main rivals, Tottenham Hotspur, Manchester City, Manchester United, Liverpool and Arsenal, made significant investment in their squads.
"It is very difficult for every team in this league. To defend – it is very difficult to win two titles in a row," Conte said.
"We won the title with Juventus and I was expecting a really strong challenge from AC Milan, but instead they sold Zlatan Ibrahimovic and Thiago Silva to Paris St Germain, so they became weaker. It wasn't simple second time, but it was easier.
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"Here, from last season to this season, you have big teams and now they are bigger... And now after I think a great transfer market, they have improved a lot. It's not simple to play this league."
City and United splashed out in the last transfer window and the two Manchester clubs lead the league table on 19 points from seven games, followed by Tottenham in third.
Chelsea dropped to fourth, six points behind the leaders, after losing 1-0 to City on Saturday and the defeat was compounded by a muscle injury to striker Alvaro Morata.
Conte's team travel to basement side Crystal Palace, who are yet to win a league game this season, on Oct. 14.
(Reporting by Aditi Prakash in Bengaluru, editing by Ed Osmond)
