Serena already best ever: McEnroe

Serena Williams does not need to win the calendar Grand Slam to prove she is the greatest ever female tennis player, says John McEnroe.

The 33-year-old, two victories from winning the first calendar Slam since 1988, plays Roberta Vinci in Friday`s delayed US Open semi-finals.

The first semi-final is between Simona Halep and Flavia Pennetta at 16:00 BST.

"She`s the greatest female player I`ve ever seen," McEnroe told BBC Sport. "She`s proven it to me over and over."

The men`s semi-finals will get under way at 22:00, with Novak Djokovic against Marin Cilic followed by Roger Federer against Stan Wawrinka, but it has been Williams in the spotlight throughout the tournament.

The world number one currently holds all four Grand Slam titles, and another victory in New York would take her to 22 majors.