Canada's Bianca Andreescu withdrew from the US Open on Saturday, the 2019 singles champion missing the event for the second time since winning in her debut at 19, organizers announced.
She will be replaced in the draw of the year's final Grand Slam tennis tournament by a qualifier or lucky loser when the tournament begins on Monday.
Andreescu revealed earlier this month that she had been diagnosed with a "small stress fracture" in her back. She also withdrew from last week's final major US Open tuneup at Cincinnati,
Andreescu said she began to feel pain at the Washington Open and worked to play at Montreal the following week, but struggled in a first-round loss to Italy's Camila Giorgi.
In the US Open draw, Andreescu had been slated to open against 2018 US Open quarter-finalist Lesia Tsurenko of Ukraine.
Andreescu made a stunning run on the New York hardcourts in 2019, defeating Serena Williams in the final but missing out on the Flushing Meadows fortnight the following year due to the Covid-19 pandemic.