The 30-year-old has won 14 Grand Slams in a glittering tennis career, but the last came at the French Open in 2014 and his 2016 season was ruined by a wrist problem.
Many believe he is past his peak but Nadal still has faith as he prepares for the Australian Open in Melbourne next week.
"If I believed that if (I) could not have this chance during this next 11 months, I would be home fishing," he told reporters in Sydney Monday ahead of a Fast4 exhibition event.
"My real goal is to try to compete for the important things and to compete for the important things I know I have to try to beat these guys," he added, referring to Andy Murray and Novak Djokovic.
"If I am working hard and I have the motivation and passion to keep going, I feel that if I am happy and I can work the way I want to be, I can be."
After opening his season in Doha for seven of the past eight years, Nadal instead opted this year to begin at the Brisbane International in a bid to better adapt to the Australian conditions.
But he lost in the quarter-finals last week to big-serving Milos Raonic, and has slipped down the world rankings to nine.
Despite this he is confident ahead of the opening Grand Slam of the season, where he lost in the first round last year and has only won one of his major titles.
"I feel that Melbourne is an opportunity to play well again and to have positive feelings and then anything can happen if I start to feel good and competitive," he said.
"I love playing in Melbourne. It's an unbelievable event. I'm very excited to come back. Last year was a tough year and I just hope to change things this year and play better again."