The striker netted 15 goals last term, but only once since the turn of the year, as Spurs narrowly missed out on Champions League qualification for the second season running.
And with Emmanuel Adebayor adding just five further goals, Defoe believes Spurs need to invest in another forward - with Goal revealing the club are unwilling to meet Aston Villa's £25 million valuation for wantaway striker Christian Benteke.
|4/7||Tottenham are 4/7 with BetVictor to sign Christian Benteke
"When Manchester United won the treble in 1999 they had unbelievable forwards like Andy Cole, Teddy Sheringham, Ole Gunnar Solskjaer and Dwight Yorke - you need that.
"If you want to do well it's important to have competition. It will definitely help us to bring more goals into the team."
Defoe, meanwhile, brushed aside speculation regarding his future at White Hart Lane and admitted he is focused on scoring goals to secure a spot in the England squad for next summer's World Cup.
"People say 'This club's in for you, that club's in for you' but I don't take any notice," the 30-year-old added.
"If someone comes in for you, your agent will tell you. It goes over my head. It's happened for years. All I can say is I was doing the kit thing so it looks like I'll be wearing it for the season.
"In a World Cup year it's important for me to play. It's based on merit. People will look at me and ask how many goals have I scored? To score goals you've got to play.
"I've got to score a lot of goals this season to get into the squad. A top club brings in top players. When you've something to fight for, you get the best out of yourself."