Roger Federer's intended return to tennis at the Miami Masters has fizzled as the Swiss withdrew with a stomach virus shortly before his second-round match with Juan Del Potro.
The world No.3, who was to have played his first match in seven weeks after undergoing knee surgery in Switzerland, was replaced in the draw by Horacio Zeballos of Argentina.
Federer owns two Miami titles, the last one in 2006. His next event should now be the Monte Carlo Masters on clay from April 10.
"I am very sorry that I have to pull out of the Miami Open with a stomach virus," Federer said. "I feel bad for the tournament and the fans as I have rarely ever had to withdraw at such short notice.
"I've 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 I am in no condition to play. I tried to warm up this morning but it was clear that I could not compete."