Novak Djokovic reflects on relationship with Federer and Nadal, calling their rivalries eternal in tennis history.

Novak Djokovic is opening up about his relationship with fellow tennis stars Roger Federer and Rafael Nadal, admitting that it's often strained.

In his bid to land a 25th Grand Slam, the 37-year-old has enlisted the help of Andy Murray, an opponent he faced 36 times and who knows as much as anyone about the strengths of his game.