Basketball-mad tennis bad boy Nick Kyrgios says he learnt a lot about how to compete from watching NBA great Kevin Garnett.

The 21-year-old Australian revealed the extent of his passion for the team sport and the NBA’s Boston Celtics in an article for The Player’s Tribune.

In the piece titled, “Why I Bleed Green”, Kyrgios says Garnett, who used to play for the Celtics, is his “spirit animal”.

The 39-year-old Garnett, a 15-time All-Star, currently plays for the Minnesota Timberwolves but previously played for the Celtics from 2007-13.

“He’s my favourite player ever,” Kyrgios wrote.

“Every guy wants him on their team, but nobody wants to face him. He’s so intense.”

“As a tennis player, there’s a lot I’ve learned from how insanely competitive KG is, even now, when he’s 39 years old, he’s still a maniac.

“He might offend some people, but at the end of the day, sport is about winning or losing.”

The World No.20 said he watched NBA games as much as possible while on tour and liked to match other tennis players with NBA equivalents.

“Roger Federer? Oh, he’s Ray Allen, bro,” he wrote.

“So professional, day in, day out. He just gets the job done. He’s a Ray Allen for sure.”

Kyrgios said people on tour see him streaming NBA games on his phone in the weirdest places and ask why he’s so into basketball.

“I think it has something to do with tennis being such an isolated sport,” he wrote.

“You’re one-on-one out there. What I love about playing hoops is the team aspect.”