World number two Djokovic, who has won a record 24 Grand Slam singles crowns, was last year's champion at Cincinnati, the third time he has won the event.
Djokovic has not won a Grand Slam title since capturing last year's US Open, losing in this year's Australian Open semi-finals, French Open quarter-finals and in the Wimbledon final.
On Sunday, he beat Spain's Carlos Alcaraz -- who he lost to at Wimbledon -- in the Olympic final.
"We certainly understand that it is a quick turnaround from his Olympic triumph to come to Cincinnati," said Cincinnati Open tournament director Bob Moran.
"His title run here last year was so memorable. We are eager to see him on court again soon."
The withdrawal moves Frenchman Giovanni Mpetshi Perricard into the Cincinnati Open main draw.
