Four years down, three to go for Serena Williams. It's just a matter of her toughness.

The world's No. 1 women's tennis player earlier this week surpassed Martina Hingis for fourth place all-time in weeks as the top-ranked female with her 210th week atop the WTA.

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She still has a long way to go to reach the three women ahead of her. No. 3 Chris Evert was No. 1 for 260 weeks. No. 2 Martina Navratilova spent 337 weeks as the top-ranked player. The No. 1 player in weeks spent at No. 1, Steffi Graf, spent a whopping 377 weeks as the best player in the world.

Givemesport.com is suggesting that the chances of Williams catching Graf are remote, and without that motivation, Williams, at age 33, has little else to play for.

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Injuries and illness have (affected) the world No. 1 throughout this year, contributing to disappointing showings at all the majors apart from Flushing Meadows. As Serena dips further into her (30s), such issues are only likely to become more commonplace one would expect," Givemesport.com stated. "Not now, but maybe soon, Serena should have some reflection and maybe question why she continues to put herself under strain."

To answer that is to try to figure out Williams' motivation. She is still the most imposing figure in women's tennis. Consider that No. 2 Maria Sharapova has lost 15 consecutive matches to Williams with no signs of closing the gap.

Until Williams proves otherwise, she still will be considered the player to beat in 2015. If she hangs on to the top ranking all year, she would surpass Evert and trail only Navratilova and Graf.

In 2003, she told ESPN that she didn't think she'd still be playing at age 31 and wasn't in the game to break records, and that seemed to be a rational statement at the time. A year later, she said she did want to become the greatest.

As the 2014 tennis season comes to a close, Williams' biggest motivation could be her fame. She's still relevant. She had one of the most bizarre exits in tennis history during a doubles match at Wimbledon when she couldn't catch a bouncing tennis ball or hit a serve over the net.

She said she had a viral infection, added to the buzz by posting a photo of herself in all her sickness glory on social media, and went out less than two months later and won the U.S. Open.

No player currently on the tour or on the horizon looms as her equal, but can she set her sights on a three-year commitment?

Do you think Serena Williams can catch Steffi Graf's all-time record of 377 weeks (Serena is at 210)? Comment below or tell us @SportsWN.