Defoe, 29, who scored in Spurs' opening-day defeat at Newcastle United on Saturday, is currently the only senior recognised striker at the club.
"He always has this killer instinct," said Villas-Boas. "He scored in midweek for his country, scored for us during pre-season and again [at Newcastle].
"He is showing that touch that we need up front. Jermain accepts that we are looking for one more striker because the team is in need of that, but when we have them all together the quality of the player is tremendous.
"I have nothing to do with anything that happened in the past. He is our striker, is playing extremely well, is full of confidence and has been deadly in front of goal."
Spurs officials are currently trying to negotiate a deal to re-sign Manchester City forward Emmanuel Adebayor, who spent last season on loan at White Hart Lane.