The 31-year-old moved from Tottenham to Toronto in February and has been a hit in the MLS, scoring 11 goals in 16 appearances.
Redknapp was keen to bring Defoe back to England but was unable to conclude a deal before the transfer window shut on Monday.
But he is confident on the England forward - who he has previously worked with at West Ham, Tottenham and Portsmouth - arriving at Loftus Road in January as QPR look to avoid relegation.
"There is every chance he will come in January," Redknapp told talkSPORT.
"I'm a big fan of Jermain's. Almost certainly, I think we will [go back in for him].
"I've signed him so many times. I've taken him everywhere."
"We tried all day with Jermain Defoe," he added.
"He was keen to come. We agreed a deal with Toronto but they wouldn't release him now.
"We could do a deal and then take him in January but we wanted to get someone in today."
Sandro's deal is permanent while Kranjcar has joined on a season-long loan, linking up with Redknapp for a fourth time.
