The 31-year-old has scored 11 goals since moving to the Canadian club earlier this year but was linked with a return to England during the transfer window, with QPR reported to be interested.
Harry Redknapp has worked with Defoe at West Ham, Portsmouth and Tottenham but a reunion at Loftus Road failed to materialise.
The striker is currently in England recovering from a groin injury and Leiweke is not convinced his star player will return.
"I personally don't think Defoe will come back," he is quoted as saying at Ryerson University. "I think if he doesn't want to be here, you get rid of him.
"My attitude is, if you want to be here and buy into what we’ve been doing, let's go roll up our sleeves and we'll fight together.
"If you don't want to be here, get the hell out of our way."
Toronto have not won any of their last five games and sacked head coach Ryan Nelsen at the end of August.
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