The news ended a bitter-sweet day for the struggling Premier League side who earlier re-signed Ireland forward Robbie Keane from Liverpool.
Defoe, who himself rejoined the north London club from Portsmouth last month, was injured in training last week.
"Following further scans and examination, Jermain Defoe will undergo surgery tomorrow after suffering a stress fracture in his right foot," said the Tottenham website.
"Early detection has allowed the club to opt for the best long-term treatment."
The news is a terrible blow for Defoe who will miss out for the third time in a year on a Wembley showpiece with Spurs due to face Manchester United in the League Cup final on March 1.
Last season Defoe signed for Portsmouth shortly before Tottenham beat Chelsea in the League Cup final and he was ineligible for Portsmouth's FA Cup final win over Cardiff City because he had played in an earlier round for Spurs.
The injury is also expected to sideline the striker for crucial Premier League clashes against Arsenal, Chelsea, Aston Villa, Blackburn Rovers, Middlesbrough, Hull City, West Ham and Newcastle.
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