The former Real Madrid star signed for Rayo before last night's defeat to Barcelona.
Perez said, "My experience with people who have achieved a lot at an elite level, it happened recently with (Radamel) Falcao there are two ways: either they are inaccessible to others or they fail on a sporting and human level. If he is here, it will be another way.
"James can play in all three positions. The position in which he has given his best is that of midfielder, but he can also play as an '8', as he did at Bayern Munich. He can do well in any position. He is a player who intervenes very well in the game."
James also said, "It's a great joy to be back playing in La Liga. It's incredible, a historic club like Rayo Vallecano that has a great desire to do things well. Every place I go I always have this responsibility, I'm a player who likes to win and I hope to be able to do things well in this very important year (the year of Rayo's centenary) for this fantastic club."