John McEnroe has lauded Serena Williams as the greatest female tennis player of all-time.
The American is on the verge of winning the Serena Slam - claiming all four of tennis' major titles in a calendar year.
Should she beat Roberta Vinci in today's US Open semi-final, she will be just one match away from completing the feat and McEnroe already feels that she has a special place carved into tennis history.
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In comments to the BBC, he said: "She's the greatest female player I've ever seen."
He also went on to say that he thinks "Serena is one of the all-time greatest athletes, period. Man or woman."
