Defoe was linked with a move away from White Hart Lane during the transfer window, but since he joined Spurs in the summer, Villas-Boas has placed faith in the England forward and he has been repaid with several impressive performances.
Villas-Boas said: "He has been immense for the team.
"For a striker, goals are decisive and he has four in the Premier League. He's not far off being top scorer and he has been creating so much.
"I can't put anything of his in to question. He has desire, his motivation is there, and his movement is fantastic so we hope he will continue in this way."
Defoe is expected to feature in Tottenham's match with Manchester United on Saturday evening.