Stephens was seeded fourth in the season's first clay-court event. She pulled out of the tournament Monday.
Stephens said in a statement she was sorry to miss the event, but her championship play in Miami "left me completely exhausted/fatigued both physically and mentally."
Stephens defeated Jelena Ostapenko 7-6 (5), 6-1 to win the Miami tournament.
Stephens, 25, said she did not feel ready to play her best tennis and decided it was in her best interest to get some rest.
The American won her first major, the US Open, last September.
Most of the top seeded players, including No. 1 seed Caroline Garcia of France, will begin play on Tuesday.