Tottenham defend Defoe sale to Portsmouth
Defoe had 18 months left on his contract at White Hart Lane and there had been no progress in agreeing an extension while his first-team opportunities were limited.
"The club reluctantly agreed the transfer of Jermain in light of there being less than 18 months left on his contract," read a statement from Spurs.
At the start of the season Martin Jol, manager at the time, highlighted Defoe's contract situation as a concern for chairman Daniel Levy.
Campbell left for nothing in 2001 to rivals Arsenal and Levy wanted to avoid a repeat with Defoe.