Pep Guardiola (right) has given his backing to Barcelona manager Ernesto Valverde
Valverde replaces Luis Enrique in charge of Barcelona from next season.
The former Barca player arrives at the Nou Camp following four years at Athletic Bilbao.
And Guardiola – who oversaw the most successful era in Barcelona's history – says La Liga and Champions League winners Real Madrid should be wary of a Barca revival.
"I congratulate Real Madrid because they were the worthy winner of the Champions League, but I would also tell them not to become overconfident because Barcelona always bounce back," Guardiola said during a Johan Cruyff Foundation day via FourFourTwo.
Barcelona have made a strong choice
Guardiola on Valverde
"Ernesto is an exceptional Coach and a good friend.
"Barcelona have made a strong choice."
Guardiola guided his City side to a third-place finish in the Premier League – his first season in English football.
He won three La Liga titles while at Barca and twice steered them to the Champions League.
Real boss Zinedine Zidane now has two Champions League titles to his name as a manager.
Valverde has become Barcelona's new boss
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Zinedine Zidane steered Real Madrid to Champions League glory on Saturday
And Guardiola reserved praise for the Frenchman.
"He is a great coach and, as a player, he was on another level," Guardiola said.
"I am happy for him because he has done an excellent job."