On court, he was one of the most aggressive players of all time.

But John McEnroe, whose foul-mouthed tirades earned him a reputation as a tennis bad boy, has shown a sensitive side in retirement– revealing he is ‘proud to be a feminist’.

The US star, 58, made the remark as he criticised the gender pay gap in modern professional tennis.

John McEnroe has criticised the gender pay gap in modern professional tennis

Although each of the four Grand Slam tournaments offer the same prize money for men and women, there is a huge discrepancy between the annual earnings of the game’s top male and female players, with men far out earning women.

Asked about the issue, McEnroe told the Sunday Times: ‘Now I have daughters, what happens in women’s sports matters to me. I am proud to be a feminist.

‘I’m often asked about equal prize money and whether women “deserve it”.

‘My response is to make a comparison: just because a film goes on for three and a half hours doesn’t mean it’s better than the one that lasts 90 minutes.

‘Just because the guys play best of five doesn’t mean we should get 40 per cent more money.’

John McEnroe playing with Maria Sharapova. He says his daughters have made him care more about women's sport

McEnroe, who retired having won seven Grand Slam singles titles including three Wimbledon championships, returns to the All England Club next month in his regular commentary slot for the BBC.

With his wife Patty Smyth, the US singer-songwriter, he has two daughters, Ava, 18, and Anna, 21.

The father-of-five also had three children, sons Kevin, 31, and Sean, 29, and daughter Emily, 26, with his first wife Oscar-winning actress Tatum O’Neal, 53.

The pair divorced in 1994 after eight years of marriage before McEnroe went onto marry Miss Smyth in 1997.