In an interview with ESPN UK, Serena Williams’ coach Patrick Mouratoglou says that his charge needs things to keep her motivated at the age of 33.

Read the full interview at ESPN

Re-writing tennis’s history books, naturally, is a pretty nice carrot to dangle.

"I think, as a player, you need to play for something,” Mouratoglou told ESPN. “Serena has won everything in tennis in singles and doubles. She loves the sport and still enjoys playing a lot but that is not enough to stay competitive. Everyone needs a goal. Writing tennis history is a very motivating goal for her."

Williams will bid for her 20th career Grand Slam title at Roland Garros, which begins this Sunday. After passing Chris Evert and Martina Navratilova at this year’s Australian Open (and tying Helen Wills Moody), Williams now needs three major titles to draw level with the great Steffi Graf. After that, the only woman to catch is Margaret Court, who won 24 major titles.

When asked what it would mean for Serena’s legacy to catch Graf, Mouratoglou said: "That would be incredible. Steffi's record looks unbeatable. If Serena manages to do that, that would probably be the best proof that Serena is the greatest player of all times."

Though Williams has been atop the WTA Rankings for 241 weeks total, and 117 weeks consecutively, her coach says that Williams is still improving. "Serena can still improve a lot,” he said. “That is what is beautiful in this sport. Even the best player in the world has a room for improvement. I can't tell you what we are working on at the moment, but I can tell you that you will see it soon or later when you watch her matches."