Recent reports had suggested that Spurs had joined North London rivals Arsenal in the pursuit of the Spanish international, who has played just 64 minutes so far this season.
However, Villas-Boas has insisted that because Tottenham are a direct opponent to Chelsea, the Blues will have no intention of letting the 25-year-old sign on at White Hart Lane.
"Chelsea wouldn't sell to Tottenham as they think that we are title contenders. The other thing is that Mata is a great, great player and a very, very important player for Chelsea. They are not going to strengthen another side, that in their opinion, plays for the title," the head coach told reporters.