World No. 5 Caroline Wozniacki, who is just 17-7 in 2015, is hoping to snap out of a slump during the clay-court season. The Dane failed to reach the quarterfinals at both Indian Wells and Miami, and recently added four-time Grand Slam Champion (and three-time French Open champion) Arantxa Sanchez-Vicario to her team. The Spaniard has not coached much before, except in Fed Cup for one season in 2012.

Last year, Wozniacki only played two tournaments on clay, losing in the second round of Madrid and in the first round at Roland Garros.

"We've been working on more about the mentality going into the game and going onto the surface," Wozniacki said. "You have to hit more balls into the court, you have to run more balls down and change up the pace, and that's really it. My game really should fit with clay, but I haven't had the results I've wanted. I'm trying to do my best to change that."

Wozniacki is playing Stuttgart this week and will face Lucie Safarova in her first match.

She said that she hasn’t decided whether Sanchez-Vicario will continue with her after the clay-court season. Her main coach is her father, Piotr.