The Frenchman played in yesterday's derby defeat at Arsenal and told the Mirror: "When you arrive, it is a new country and a new mentality. It is not the same as in France. You need some time to adapt. Here you play very quickly and there's never a break during a game. It's always a fight. I like this style.
"When you come to England, you have to build yourself up because the game is very physical. At the start I went into the gym as well and put on a couple of kilos of muscle."
Hailed as the "best young centre-back in Europe" after his £7.8m summer signing, he was slated as one of the final pieces in a young team ready to make the push into the top four under Martin Jol. Instead a series of horrific defensive team displays saw the Dutchman replaced by Spaniard Juande Ramos and Kaboul even "rested" for the UEFA Cup tie in Anderlecht earlier this month.
"It was something that had to be done," he admitted. "The manager explained he wanted to leave me behind to get some rest.
It gave me a rest and it worked. It was a good decision.
"I lost a little bit of confidence. It's clear that in the game against West Ham I was a bit disappointed in the way I played. But since then I have returned to my level and concentrated on playing well.
"This is football. You can't always do your best. Sometimes you are a little tired. Sometimes you are good."