Antonio Conte believes Tottenham are "paying" the price for not replacing key players since he left his role at Chelsea.
The current Spurs manager was in charge of the Blues between 2016 and 2018, when Tottenham were at their peak under Mauricio Pochettino.
The Argentine's side finished second in the Premier League behind Conte's Chelsea in 2017, reaching the Champions League final two years later.
But since the Italian's last spell in England, Tottenham's greatest team in a generation has fallen apart.
Kyle Walker, Mousa Dembele, Kieran Trippier, Christian Eriksen, Victor Wanyama, Danny Rose, Erik Lamela, Toby Alderweireld and Jan Vertonghen have all left the club.
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Tottenham chairman Daniel Levy has attempted to replace these stars - spending more than £350million on players since 2017 - but his investments haven't worked out as hoped.
The faltering team finished sixth and seventh in the Premier League the last two seasons and face a battle to qualify for the Champions League again.
Spurs are currently ninth in the table, 14 points behind leaders Chelsea with two games in hand.
Speaking ahead of his team's home fixture against Premier League rivals Brentford on Thursday evening, Conte criticised the club's recent business.
"The club, in the last years, has been slipping," said the Italian via Sky Sports News.
"If I compare Tottenham to when I was in Chelsea, Tottenham was very, very competitive, was a really, really strong team.
"And I think that to lose important players or someone became old and then to have a change of generation, I think Tottenham now is paying a bit of this."
Pochettino often urged Levy to invest in the squad during his time at Tottenham to help the team end their long wait for success.
"After nearly five years the club is on another level than five years ago, but how we operate in four or five years didn't change," Pochettino told ESPN in January 2019.
"That is the point when sometimes people talk about winning titles.
"One thing is to reduce the gap with the top four, to be competitive, to create a team capable of fighting with the big sides. But if after we want to win titles we need to operate in a different way.
"Of course, maybe we can win some titles but it's going to be a tough job to do because in that situation every club in the last five years was improving a lot.
"The other day I saw a stat, in the last 10 years in England and in Europe how the teams were spending money, and I think we were on the bottom, in England and Europe.
"Of course we're doing a fantastic job but if we want to be real contenders we need to operate in a different way in the future."
Conte succeeded Nuno Espirito Santo as Spurs manager last month and has endured an indifferent start to his tenure.
The Italian has won two of his four games in charge in all competitions, suffering an embarrassing 2-1 defeat to Slovenian minnows Mura in the Europa Conference League.
Conte believes making Tottenham competitive again is the "biggest challenge" of his illustrious career.
"We have to create, start again," he added. "We have to create a solid base and build to come back and fight for something important as in the past. We must be honest.
"But it doesn't mean we don't want to think great. We need to think great. But, in this moment, we have to know we are here."
