Van Ginkel joined the Blues from Vitesse Arnhem last week, putting pen to paper on a deal that will keep him at Stamford Bridge until at least 2018.
"Marco is one of the best prospects in European football right now," Mourinho told reporters. "I have been following him for a long time. He has great potential.
"We do not have to press him too much in the beginning because we want to help him settle into the Premier League. Chelsea is investing in the long term and this kid has a great future."
Chelsea were forced to fight off interest from Ajax for Van Ginkel, who has made one appearance for the Netherlands national team.