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Roger Federer has withdrawn from the Miami Open after being struck down by a stomach virus.
Tournament organisers announced the Swiss had been pulled ahead of Friday's second-round meeting with Juan Martin del Potro.
World number three Federer, a winner of the tournament in 2005 and 2006, will be replaced by lucky loser Horacio Zeballos.
"I feel bad for the tournament and the fans, as I have rarely ever had to withdraw at such short notice," Federer said in a statement.
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"I have not felt great for a few days, and unfortunately it got worse in the last 24 hours. I was really excited to have my comeback in Miami but am in no condition to play. I tried to warm up this morning, but it was clear that I could not compete."
Federer, a 17-time grand slam champion, had been due to make his return in Miami after undergoing surgery on a knee injury.
The 34-year-old revealed this week that he suffered a torn meniscus while preparing a bath for his twin daughters.