John McEnroe and Serena Williams

New York: Serena Williams, a 23-time Grand Slam singles champion, fired back at John McEnroe's remark that she would only rank about 700th on the men's tennis circuit.

McEnroe, a seven-time Grand Slam singles winner, called Williams "best female player ever -- no question," in comments to National Public Radio aired Sunday. McEnroe then went on to explain why she should not be considered the best of all time.

"If she had to just play the circuit -- the men's circuit --that would be an entirely different story," said McEnroe.

Speaking on a tour to promote his new book, the former 'brat' of world tennis said, he would place Williams "like 700 in the world" on the ATP Tour. Williams responded to McEnroe in two Twitter postings. One read: "Dear John, I adore and respect you but please please keep me out of your statements that are not factually based." In another she said: "I've never played anyone ranked there nor do I have time. Respect me and my privacy as I'm trying to have a baby. Good day sir."

Williams, 35, won this year's Australian Open for her seventh Melbourne crown and her 23rd Slam singles title, setting an Open Era record and moving one shy of Margaret Court's all-time Slam singles title record.

In April, Williams announced that she was pregnant and would not compete for the remainder of the season. Williams has won Wimbledon and the Australian Open seven times, the US Open six times and the French Open three times. McEnroe, 58, is a former World No. 1 like Williams. He won four US Open and three Wimbledon singles titles.