RAFAEL NADAL says he will work on the mental side of his game as he begins preparations for the clay-court season.

The 28-year-old crashed out of the Miami Open with a three-set defeat to Fernando Verdasco on Sunday.

It ended a disappointing few weeks in the USA after he lost in the quarter-finals of the BNP Paribas Open at Indian Wells to Canada's Milos Raonic.

The Spaniard did win a low-key event in Argentina back in February but it has generally been a below-par start to the year for the 14-time Grand Slam winner.

The Majorcan has always been known for his mental toughness and he has been able to grind out results as his opponents wilted over the years. But, as he gets ready for another assault on the French Open and other clay-court tournaments, the nine-time Roland Garros champion admits that he still has much to work on.

"I need to fix again the nerves, the self-control on court. It's not a tough issue to fix. I'm going to keep trying," he said.

"I'm practising with the right attitude, I think. I'm arriving at an important part of the season for me on the clay.

"I've been able to be under control, control my emotions during, let's say, 90 per cent of my matches," he said.

"However, it is being tougher to be under self control. But I'm going to fix it. I don't know if in one week, in six months, or in one year, but I'm going to do it."