Miami - World number five Milos Raonic pulled out of the Miami Open on Sunday with a recurrence of a hamstring injury - the latest fitness blow to hit the Canadian.
Raonic originally suffered the injury in the semi-final at Delray Beach and was forced to forfeit the final against American Jack Sock. He then missed this month's Masters event at Indian Wells.
The 26-year-old returned to action in Miami on Friday with a win over Serbian Viktor Troicki but said his injury had flared up again.
"It is the same muscle in the hamstring it got progressively worse after my first round and after practising yesterday (Saturday), it was not possible to compete today without putting myself at significant risk," he told reporters.
Raonic was due to face American qualifier Jared Donaldson.
His exit means three of the top five players in the world have had to sit out Miami due to injury. World number one Andy Murray and number two Novak Djokovic pulled out before the tournament.