Serena Williams confessed to being unhappy with her form in 2016, suggesting a record of three final appearances from four events is not good enough as she prepares for the French Open.

Williams suffered defeat to Angelique Kerber in the Australian Open final in January before losing to Victoria Azarenka in Indian Wells two months later.

The American was beaten in the round of 16 by Svetlana Kuznetsova in Miami in March but, after missing the Madrid Open through illness, she claimed her first title of the year in Rome last week.

The world number one believes that would be enough to satisfy most players on the Tour, but she expects more from herself.

"It felt good to win in Rome, obviously. I was feeling pretty confident," said Williams.

"For me, if I'm not winning, I'm not happy about my year. Four tournaments and three finals isn't bad for everyone else.

"Then again, I'm not everyone else. So that's just kind of how I look at it.

"For me, when you win all the time, if you play in tournaments without winning it's kind of like a drought."

While suffering from a virus, Williams had to play five three-set matches en route to the Roland Garros title in 2015.

The world number one suggested she would not be able to replicate such a feat of endurance this time around.

"I still don't know how I got through that. Of all titles, it was crazy that I was able to win this one last year," continued Williams.

"This time I'm taking vitamin C every night. If it happened again, I'm not sure I could get through that again."

Williams will face Magdalena Rybarikova in the first round of this year's French Open.