Modric has been linked with a move to Chelsea for much of the summer and Redknapp is reluctant to let the Croatian playmaker leave.
However, Redknapp believes that selling the 24-year-old would provide him with the funds he needs to make Tottenham a better team.
"He's had his head turned. I want to see him here at the start of the year, but if he goes then you get three or four players [in]," said Redknapp.
"They're your options - get the money and get four players and, in all honesty, have a better team, or keep Luka, who is a fantastic player."
Adebayor scored 46 goals in 105 appearances for Arsenal during his time at the club from 2006 to 2009.