Raonic, ranked 20th in the world, played the Italian Open last week and was eliminated in the second round.
Meanwhile, women’s world number 10 Bencic was knocked out in straight sets in her first match in Rome after getting a bye into the second round.
Bencic’s withdrawal means only six of the top 10 ranked women’s players will compete at Roland Garros, with defending champion Ash Barty, U.S. Open champion Naomi Osaka and Bianca Andreescu skipping the tournament.
Spain’s Fernando Verdasco was also a late withdrawal.
The French Open, usually held in May-June but postponed this year due to the COVID-19 pandemic, begins on Sunday.