World number one Caroline Wozniacki has dropped her father Piotr as coach in a dramatic attempt to halt a worrying slump in form just 11 days before the start of the US Open. "I am no longer her coach. Who will be the new one? I promised I wouldn't say," Piotr Wozniacki told the Ekstra Bladet newspaper. The pair agreed to make the change, he said, after Wozniacki's third consecutive fourth-round exit at Wimbledon earlier this year. Since then, she has lost both her openers at the Toronto and Cincinnati events, the traditional tune-ups before the US Open, the season's final Grand Slam event, which gets underway on August 29. "From morning to night, we have heard how Caroline should play. Now we are trying something else. I am Caroline's father and I will always support her," said Piotr Wozniacki, a former professional footballer.