Former British number one Laura Robson lost 7-6 (7-4) 6-2 to Belgian Kirsten Flipkens in the first round of the Miami Open on Tuesday.
Robson, 22, has struggled with a wrist injury over the past 18 months and made her first appearance since August at the BNP Paribas Open on 11 March.
She lost to Magdalena Rybarikova in the first round at Indian Wells.
Meanwhile, British wildcard Katie Swan lost 6-2 4-6 6-2 to American Sam Crawford in qualifying.
The 16-year-old had beaten world number 102 Lauren Davis but struggled with a tight hamstring against Crawford.
Fellow Briton Naomi Broady also went out in the final round of qualifying, losing 6-4 6-2 to Belarusian Aliaksandra Sasnovich.
James Ward failed to join compatriot Andy Murray in the main draw of the men's event, losing 6-3 6-3 to American Bjorn Fratangelo.
Swan, who is from Bristol but based with her family in the United States, only recently turned professional after choosing tennis over university.
The teenager, who turns 17 on Thursday, fought back to level against Crawford before succumbing in the final set.
"My hamstring started to get really tight and I saw the physio at the end of the set and she taped it up," Swan told BBC Sport.
"It was pretty tight when I was pushing up on my serve, which affects me a little bit."
She added she had learnt a lot from her experience in Miami.
"I'm really glad that I got the chance to play this week because it made me realise I do have the level to compete with the top players," she said.