De Bruyne, 34, left City at the end of last season when his contract was not renewed and joined Napoli, who visit the Etihad Stadium for their Champions League group opener on September 18.
"I've only played two matches in Serie A. It's different under manager (Antonio) Conte than the years under Pep Guardiola," De Bruyne told reporters on the eve of Belgium's World Cup Group J qualifier against Kazakhstan in Brussels.
"My first impression is that it's more tactical in Italy and things move a bit slower. But it's still football.
"I played other systems before while at Manchester City," he added, fielding more questions about his club career than the World Cup clash.
"We're playing against City in Manchester with Napoli soon. That's going to be strange. City is my club and that's not going to change," De Bruyne added.