"Steffi Graf's going to destroy another teenager, Martina Hingis is a basket case": When John McEnroe spoke on Graf's Wimbledon clash vs Kim Clijsters

John McEnroe once predicted that Steffi Graf would "mentally destroy" a teenaged Kim Clijsters in their clash at the 1999 Wimbledon Championships. The American made a cheeky reference to Graf's dominance over Martina Hingis to back up his claim.

That year, McEnroe and Graf formed a blockbuster mixed doubles partnership at the grasscourt Major. The duo made for a formidable team, claiming a clinical 6-2, 6-4 win over Jeff Coetzee and Eva Melicharova in their opening match.

In addition to their strong on-court partnership, John McEnroe and Steffi Graf also developed a friendly bond off the court, sharing a laugh when the American poked fun at Melicharova's serve in their post-match press conference.

The conversation then shifted to Graf's singles campaign, with the German being asked for her thoughts on her fourth-round clash against 16-year-old qualifier Kim Clijsters, who was making her Grand Slam debut at Wimbledon.

While Steffi Graf provided a thoughtful analysis of Clijsters' playing style, John McEnroe interjected to predict that the German would "mentally destroy" another teenager, asserting that she had already reduced Martina Hingis to a "basket case" despite being much older than the Swiss at 30 years of age.

"Steffi is going to destroy another teenager mentally. (Martina) Hingis is a basket case. You see, it's nice to be 30," he said (via the Irish Times).

Graf dominated her rivalry with Hingis, triumphing in seven of their nine encounters, including a 4-6, 7-5, 6-2 victory in their latest meeting in the 1999 French Open final.

McEnroe's comment was especially pointed, given that Hingis had suffered a shock 6-2, 6-0 loss to qualifier Jelena Dokic in the opening round at Wimbledon, despite being the top seed and fresh off a runner-up finish at Roland Garros.

The American's prediction also proved accurate, as Steffi Graf dominated her clash with Clijsters, claiming a 6-2, 6-2 win over the 16-year-old to book her place in the quarterfinals.

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Steffi Graf angered John McEnroe by withdrawing from Wimbledon 1999 mixed doubles SF after reaching singles final

John McEnroe (left) and Steffi Graf at Wimbledon 1999 (Source: Getty)

Steffi Graf and John McEnroe's mixed doubles partnership at the 1999 Wimbledon Championships progressed smoothly, as the duo advanced to the semifinals without dropping set.

They were scheduled to take on the third-seeded team of Jonas Bjorkman and Anna Kournikova for a place in the final. However, Graf made herself unavailable for the match, choosing to prioritize her singles campaign, where she had set up a blockbuster title clash against Lindsay Davenport.

McEnroe didn't take kindly to Graf's last-minute withdrawal, admitting that her decision had angered him immensely, in his book 'You Cannot Be Serious.' He also disclosed that his frustration resulted in an outburst in the locker room, which was witnessed by Andre Agassi and his coach Brad Gilbert.

Graf also endured disappointment at SW19, suffering a 6-4, 7-5 defeat to Davenport in the final. The loss marked the German's last match at the grasscourt Major.