Britain's Emma Raducanu has withdrawn from the Miami Open with a lower back injury, tournament organisers said on Tuesday, the latest setback for the 21-year-old.
Raducanu spent eight months out with wrist and ankle problems last year but returned to action in January and had an encouraging performance at Indian Wells last week where she reached the third round.
"I have been experiencing lower back pain and at this stage of my return to competition I don’t want to risk anything happening," said Raducanu.
"I really tried my best to be ready and I’m sad to be pulling out of Miami as it’s a cool tournament but wish the event all the best."
The 2021 US Open winner, a wildcard entry at Miami, was scheduled to play China's Wang Xiyu in the first round on Tuesday.
Raducanu had surgeries on her ankle and both wrists during last year.
She was beaten in the Indian Wells third round by world No 2 Aryna Sabalenka.
Wang will now face Slovakian qualifier Anna Karolina Schmiedlova.
Tuesday's action sees Romanian Simona Halep return to action after her four-year doping ban was reduced to nine months and she was cleared by the Court of Arbitration for Sport for an immediate return.
Halep, given a wildcard entry, will take on Spain's Paula Badosa.
Venus Williams takes on Russian Diana Shnaider in the first round.