Novak Djokovic has revealed that he would struggle to play his brother in a professional tennis match after admitting that he "admires" the rivalry of the Williams sisters.

Serena and Venus will meet each other for the 27th time on the WTA Tour when they clash in the US Open quarter-finals, but Djokovic has insisted that he would struggle to face his brother in a competitive match.

The 28-year-old is quoted by ESPN as saying: "The first thing that comes to my mind is how would I feel to play my brother, and I don't think that would be possible, honestly. I, in a way, admire what they're doing, for so many years to play against each other on such a big stage.

"It's strange. They are sisters. They live together. They grew up together playing tennis. Of course they love each other, but then very have to be professional and go out on the court and play each other so many times in the finals of Grand Slams, in the biggest matches.

"I applaud them for that, but I don't know if I'll be able to play my brother. It's not possible. I would not be able to handle that on the court."

Djokovic will play Feliciano Lopez in the last eight of the men's competition.