Top-seeded Milos Raonic has withdrawn from the Delray Beach Open final because of a hamstring injury, handing the title to American Jack Sock.

The 26-year-old Canadian, the fourth-ranked player in the world, slightly tore his right hamstring on Saturday night in his semi-final victory over Juan Martin del Potro which forced him to pull out on Sunday.

“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.”

The third-seeded Sock wound up with his second title of the year and moved up to a career-best 18th in the ATP rankings.

The 24-year-old also won the Auckland Classic last month in New Zealand and helped the US reach the quarter-finals of the Davis Cup.

Sock’s only loss of the year was to Jo-Wilfried Tsonga in the third round of the Australian Open.