The Spaniard will not play the final Slam of 2024.
The Italian missed the ranking cutoff, but gets a wild card into the main draw.
Milos Raonic withdrew from Montreal and may never return to his home tournament.
Men's and women's champions will earn each $3.6 million, first-round comes with $100,000 pay day.
"We want to show how much we respect what Novak has accomplished, and also attract tourists,” Serbian President Aleksandar Vučić said.
Defending WTA Finals champion Iga Swiatek is first player to qualify for season-ending event.
A pair of former Grand Slam champions lead Cincinnati women's wild cards.
