'Still a lot of work left to do'

Maria Sharapova's battle to rediscover her best form continued to be an uphill one as she came up short against Dutchwoman Kiki Bertens in the Madrid Open quarterfinals on Thursday.

The Russian former world number one has shown only flashes of the play that has earned her five Grand Slam titles since returning from a doping ban last year.

She arrived in Madrid on the back of three consecutive first-round defeats and while three wins on the Spanish clay hinted at better things the 31-year-old said there is still a way to go as she gears up for Roland Garros.

Despite a strong start 2014 Madrid champion Sharapova wilted under the powerful hitting from unseeded Bertens, losing 4-6, 6-2, 6-3.

"I look at these types of matches, I see a lot of things I should be better at, I should improve at," Sharapova, languishing down at 52 in the rankings, told reporters.

"I think it's a combination of, yes, taking the positives, but also being a little tough on yourself and expecting a little bit more from yourself.

"You can't keep giving yourself a pat on the back. It was great to get those wins against those few players. But there's a reason I came up short today.

"I go back to the drawing board and start over again."

Sharapova looks unlikely to be seeded on her return to the French Open where she has won the title twice.

Last year organisers declined to give her a wildcard after she returned from a 15-month doping ban for testing positive for heart drug meldonium at the 2016 Australian Open.

She has managed only one title since returning and split with long-time coach Sven Groeneveld after losing in the first round at Indian Wells in March.

She said she was still driven to improve and did not regret the split with Groeneveld.

"Post Indian Wells was a tough few weeks for me, I think I don't know many people that would be like, 'Let's keep going'," she said. "It was really tough. I was willing to make changes, willing to get back out there, willing to put in the work.

"I think that attitude certainly helps, that perspective on things. When you try to make the right decisions for yourself in a very selfish sport, maybe somehow in the end it works out."