Rafael Nadal says he would be fishing at home in Mallorca by now if he did not believe he could challenge for further grand slam titles.
Nadal's last slam success came at Roland Garros - the venue for nine of his 14 triumphs - in 2014 and he was plagued by injury last year.
The Spaniard's time away from the court has seen him slip to ninth in the world rankings, well adrift of Andy Murray and Novak Djokovic - the current top two.
However, ahead of his first outing of 2017 at the Brisbane International, Nadal insisted he still feels capable of winning one of tennis' premier events.
Asked if he could challenge for slams again, Nadal initially replied: "I cannot tell that because as I said before I cannot predict the future."
He then added with a smile: "The only thing that I can say, if I am healthy, I believe that I can do it. If not, I would be at home fishing."
After ending his 2016 season prematurely due to a wrist problem, Nadal made an encouraging return to action at last week's Mubadala World Tennis Championship in Abu Dhabi, winning the exhibition event.
"I am happy to be back in competition again," said the 30-year-old.
"I worked a lot in Mallorca for a month and a half, I prepared myself as much as I can in terms of physical performance. I'm just excited to compete again. Abu Dhabi was a good start and I need to continue that way."