McEnroe's revelations about Borg's retirement: "I thought it was a joke".

In the late 70s and early 80s, John McEnroe and Björn Borg established themselves as the best players in the world.

The two men met fourteen times on the ATP circuit (7 wins apiece). However, the Swede decided to call time on his career at the age of 25.

The American player revealed the background to this announcement, which he clearly found hard to believe.

"At the end of 1981, I had just completed my first season as world number 1.

A month after the US Open final, Borg and I were in Australia for an exhibition, drinking a beer before a press conference.

Vitas Gerulaitis was with us, and Borg told us he was going to stop playing. I thought it was a joke, that he was playing a practical joke on us.

At the time, we laughed," McEnroe elaborated in Andy Roddick's podcast.

"Apparently, he was serious and we said, 'What the hell are you going to do with your life? You're 25 years old.' I think he was the only player who could afford such an announcement.

He had earned enough money to consider spending the rest of his life without playing tennis, provided he didn't have children.

I've got six, so I had to keep working," McEnroe continues.

"It affected me a lot for almost two years. I didn't perform at the level I'd hoped.

The ambition is always to feel that you can improve your game as much as possible, but you can't do anything at any given time.

Mentally, I was just waiting for him to come back and push me to be better, as we've seen with those three guys Roger, Rafa and Novak.

They pulled themselves up, they had no choice but to improve.

But I realized at the end of 1983 that he probably wasn't coming back, so I started to wonder if it was worth it to maximize what I hoped I could do."