Rafael Nadal withdrew on Saturday from his semi-final clash with Roger Federer at the BNP Paribas Open due to a right knee injury.
Federer, therefore, will automatically qualify for Sunday's final, where he will face Austria's Dominic Thiem.
"I warmed up today and I felt that my knee was not good to compete at the level I needed," Nadal said.
"It's tough for me to accept all these things that I'm going through in my career," he added.
"My goal is to be healthy as many weeks as possible to keep playing and at the highest level possible," he stated.
"Sometimes I feel sad because I'm in a disadvantage to all my opponents due to my continued knee issues."
Nadal has also withdrawn from next week's Masters 1000 event in Miami because of the injury.
"I'm just going to keep doing the things that work well for me and accepting that sometimes these issues can happen."
"All the things that are in my hands, I am doing well. The things that I can't control, I can't control."
The world's number two tennis player voiced confidence he would be fit and ready for the Monte Carlo Masters in April.