The Spaniard joined the Serie A side last month on a season-long loan deal with the option to make the move permanent next summer.
Michu, who spent two seasons with Swansea in the Premier League, says he could not afford to wait any longer for the chance to play in Europe's top competition after being sold on the Napoli project by Benitez.
"I think it's a major leap in my career to play in the Champions League for the first time, for one of the most important clubs in Italy in front of a beautiful crowd," he told the South Wales Evening Post.
"I'm 28 and I've never had this opportunity, I couldn't wait any longer. I also wanted to try a different league and Napoli are one of the greats in Serie A.
"The fans are fantastic and I also have the chance to work with a great coaching staff.
"He [Benitez] spoke to me and explained many things about Napoli. I will do everything possible to heed his advice. The coach is one of the main reasons I joined."
Michu was a revelation in his first season with Swansea, scoring 18 times in 35 league appearances, but the 28-year-old was plagued by injuries last term and started just 15 top-flight games.