The Serb, who was thrashed by Jannik Sinner in the semi-finals at the All England Club, picked up an injury during the defeat, and also withdrew from the ongoing event in Toronto.
Djokovic last set foot on a hard court back at the Miami Open in March, and hasn't played at a Masters event since April.
The three-time Cincinnati champion's previous appearance at the tournament came in 2023, winning the title as he overcame Carlos Alcaraz in one of the greatest best-of-three set matches ever.
As a result, Djokovic is next scheduled to be at the revamped US Open mixed doubles alongside fellow Serb Olga Danilovic on August 19th, after being awarded a wildcard entry.
The Cincinnati Open gets underway on Thursday, while the US Open begins on August 24th.