Jannik Sinner enjoyed an unforgettable season marked by his first two Grand Slam titles and ending the year as world number one but the Italian heads into 2025 with the cloud of a potential doping ban still hanging over his head.

Sinner has so far managed fears that a ban might bring his career to a shuddering halt, but his mental fortitude will be tested again when he takes on the fresh challenge of defending a major title at January's Australian Open.

"I don't know how I'm going to react, how I'm going to play," Sinner said after winning the ATP Finals in Turin.

"I'm going to prepare in the best possible way. Like every event and then we see. I always say tennis is unpredictable. You never know what can happen. So it's going to be all good if mentally you're in a good place."

Born in the German-speaking Tyrolean town of San Candido near the border with Austria, Sinner spent much of his youth ploughing down the slopes on skis.

After switching focus solely to tennis a decade ago at the age of 13, however, his trajectory has all been upwards with a major surge over the last two seasons.

Entering the 2023 campaign ranked 15th in the world, Sinner captured four titles, including his first Masters tournament at the Canadian Open, and reached the semi-finals at Wimbledon and the ATP Finals title-decider.

He signed off the season by beating 24-times Grand Slam champion Novak Djokovic at the Davis Cup and hit the ground running in 2024 by dethroning the Serb at Melbourne Park en route to winning his maiden major.

He added the U.S. Open crown in September and ended the season with a 70-6 match record -- his triumphs at Rotterdam, Miami, Halle, Cincinnati, Shanghai and Turin leaving him with more titles than defeats in a superb campaign.

'INCREDIBLE SEASON'

Sinner's fellow rising superstar Carlos Alcaraz won the French Open and Wimbledon titles as the dominant duo shut out Djokovic, the last remaining active member of the 'Big Three', and put distance between themselves and the chasing pack.

"My goal was to understand what I can achieve this year. There was no specific goal of winning a Grand Slam or being number one," said Sinner.

"It's going to be the same next year: whatever we can catch, we take and the rest we learn. I think that was the mentality we approached this year with, trying to raise my level in specific moments, which I've done throughout.

"I'm happy about that because it's a nice way to finish off an incredible season. A lot of wins, a lot of titles. I believe there's still (room for) improvement ... Let's see what's coming next year. The future, nobody can predict."

Nobody saw what was coming in August.

Anti-doping authorities said Sinner twice failed drug tests in March and that he had been cleared of wrongdoing by an independent tribunal after it accepted his explanation of unintentional contamination.

With the World Anti-Doping Agency appealing that decision at the Court of Arbitration for Sport, Sinner's spectacular season retains an asterisk for the next few months with a ban of between one and two years a possibility.

Australian coach Darren Cahill, who joined his team in 2022, said Sinner had been worn down physically and mentally by the doping investigation but he has been impressed with how the 23-year-old embraced the pressure and finished the season strongly.

"It's not just about winning or losing," Cahill told Italian newspaper Gazzetta dello Sport.

"It's the way you face challenges and he does it as a champion."