The 30-year old netted a double as Spurs beat Dinamo Tbilisi 3-0 (5-0 on aggregate) in Europa League playoff qualifying on Thursday night to move to sixth on the North London clubs all-time scoring list.
Defoe has been linked with a possible departure in recent times but Villas-Boas made it clear that he has no plans to offload the White Hart Lane veteran.
"Jermain has the goalscoring ability and once again he proved it tonight," he told ITV4.
"What we are trying to do is build a strong team with strong players and everyone has to compete for a place.
"We always want to make teams stronger than before so players who are in the top five (actually sixth) of Tottenham's all-time goalscorers can only make you stronger."