World number four Andy Murray reached the Miami Masters last 16 on Sunday without hitting a ball when third round opponent Milos Raonic withdrew with a right ankle injury.
The 24-year-old Scot will tackle either French 13th seed Gilles Simon or Jurgen Melzer, the 22nd-seeded Austrian, for a place in the quarter-finals of a tournament he won in 2009.
Highly-regarded Canadian 26th seed Raonic had already been forced to pull out of the doubles on Saturday where he and South African partner Kevin Anderson had managed just three games against Michael Llodra and Nenad Zimonjic.
The 21-year-old Raonic had been in a rich vein of form in 2012, winning titles in Chennai and San Jose and making the final in Memphis.
At Indian Wells last week, he was knocked out in the third round by eventual champion Roger Federer.