Canadian world number four Milos Raonic pulled out of Sunday's Delray Beach Open final in Florida, handing American Jack Sock the title by walkover.

Raonic withdrew due to a hamstring tear in his right leg, an injury he said he had picked up while beating Argentine Juan Martin del Potro in straight sets in a semi-final on Saturday night.

"I didn't think much of it," Raonic told the Tennis Channel. "I thought it was just tightness from the match, but this morning I woke up unable to walk properly and did quite extensive treatment with my team.

"We came down to the conclusion that it was a slight tear of the hamstring in my right leg."

Sock's second ATP title of the year followed his Auckland Open victory last month.