Rafael Nadal knee problem improving

World number two Rafael Nadal has no doubts that his knee injury is getting better after pulling out of his Sony Ericsson Open semi-final.

Andy Murray received a walkover into Sunday's final following Nadal's injury but the Spaniard insists that the problem is improving.

"The tendons are much better today than three years ago," the Spaniard said.

"The treatments worked fantastic. I am more healthy with both tendons now. For the last couple of years, 2010, 2011, I was able to compete with perfect conditions for almost all the year."

The last time he retired from a match was against Murray in the quarter-finals of the Australian Open two years ago.