Sinner lifted the Toronto trophy back in 2023 - which was his first Masters title - but coming off the back of winning Wimbledon and sustaining a slight problem with his elbow, he opted to skip it this time around.
"I'm really disappointed to be missing the National Bank Open in Toronto, especially as I have such fond memories of playing in Canada," said Sinner.
"Winning that title in Toronto two years ago was the start of a really special moment for me, but after speaking with my team, I have to recover."
Four-time winner Djokovic, who suffered a crushing defeat to Sinner in the semi-finals in London, is suffering with a groin problem. Both players could return for Cincinnati, which begins straight after.
However, Indian Wells champion Draper announced that a left arm injury will keep him out until the US Open, where he reached the last four in 2024.
"After Wimbledon I picked up an injury in my left arm, nothing serious, but I have to make sure it recovers fully for the rest of the season. Unfortunately, I won’t be able to compete in Toronto and Cincinnati…. See you in NYC !" Draper said on social media.
The Toronto Open begins on July 27th and finishes on August 7th.