The England international is reportedly close to a move to MLS side Toronto FC and the young striker has been recently included in the first-team squad by new boss Tim Sherwood.
Redknapp has been linked with another raid on his former club to bolster his attack at Loftus Road - which has been largely reliant on 12-goal Charlie Austin this term - after loan moves for Tom Carroll and Beniot Assou-Ekotto.
Defoe is reportedly set to join Toronto FC, but the MLS season does not start until March and it has been suggested the former West Ham man could make a short-term switch to QPR in the meantime.
Redknapp is also an admirer Kane, who was praised by Tim Sherwood after coming off the bench in Tottenham's win at Manchester United - and Redknapp does not expect either player to drop down to the Championship.
"I would love [Defoe] on loan for a couple of months but I couldn't see a possibility of it happening and we've never discussed it," he told reporters. "Harry came on at Manchester United so I think he's in Tim's plans.
"I'd be surprised if Tim, if he loses Defoe, [lets Kane leave] as he'd only have two strikers."