The walkover will see Murray, 29, move to the top of the rankings for the first time in his career after replacing long-time incumbent Novak Djokovic.
Raonic said he had suffered a muscle tear in his right leg in his previous match, sending Murray through to face John Isner in Sunday's final.
No pressure over world top ranking, says Andy Murray
"This morning I had trouble waking up and getting out of bed. So I went to sort of clear any serious diagnosis," said Raonic, who hurt himself in Friday's quarter-final win over Jo-Wilfried Tsonga.
"Did some tests. Did an MRI half an hour ago, let's say. They found that I have a tear, Grade 1 tear in the right quad.
"Unfortunately, I'm not able to compete against Andy today in the second semi-final."
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