Scotland lose centre ahead of Tour
Dunbar, who has 28 caps, is the second player to be forced out this week after it was confirmed that captain John Barclay would be out for around six months with an Achilles injury.
The 28-year-old has suffered with injuries all season and has been restricted to just 10 appearances for Glasgow in the Pro14, with a mixture of knee, head and hamstring injuries keeping him out of this year's Six Nations.
He had only recently returned from his latest injury a month ago, making a scoring return for Glasgow against Connacht, but he was left out of the semifinal defeat to Scarlets.
It has been revealed that he has suffered a further hamstring injury that will rule him out of the three Tests against Canada, the United States and Argentina.
Edinburgh's Bennett will hope to earn a 21st cap and a first in more than a year.