LONDON (AFP) - Swiss seventh seed Belinda Bencic became the highest-ranked casualty at Wimbledon when she retired from her second round match with a wrist injury on Thursday.

Bencic was 6-4, 1-0 down to US qualifier Julia Boserup, the world number 225 making her Grand Slam debut, when she withdrew.

Bencic had only completed her first round match late Wednesday and was clearly struggling.

"It's my left wrist. I don't know what it is yet. I think I have to get it checked. It started a couple of days ago," she said.

"It just got worse. That's why I had to retire.

"I always try to go on the court to see what happens and how I feel. It just wasn't enough. I cannot play like this against such a good player."

Boserup, 24, goes on to face either Andrea Petkovic of Germany or Russia's Elena Vesnina for a place in the last 16.