Rafael Nadal launches his Indian Wells ATP Masters title defence still feeling the sting of his loss to Stanislas Wawrinka in the Australian Open final.

"It was one of the toughest moments of my career," said the world No 1 from Spain, who was hindered by a sore back in the four-set loss to Wawrinka in January.

"It's tough to be there for an hour and a half knowing you will not win. Not winning is not the most important thing - the worst thing is knowing you will not compete."