Jose Mourinho has accused Chelsea's top-flight rivals of attempting to buy their way to the Premier League title.
The Blues lifted the league crown last season by comfortably seeing off the challenge from the chasing pack.
Chelsea have so far brought in Asmir Begovic and Radamel Falcao this summer for minimal fees, while they have not spent more than £30m on a player since 2011.
Mourinho insists that the likes of Manchester City and Manchester United, who have both splashed the cash during the off-season, are now going the same way as his own side back in 2004 when Russian billionaire Roman Abramovich also spent big.
"In the beginning of Mr Abramovich coming to Chelsea, Chelsea was buying the title," he is quoted as saying by ESPN. "Now, they are buying the title. All of them, they are buying the title.
"It is up to us to be strong and to fight them and, obviously, to try and win it again, even without the big investments."
Chelsea continued their pre-season preparations by beating Paris Saint-Germain on penalties in the early hours of Sunday morning.
