"I've noted a small physical slip, especially this year," said Ferrer, who celebrated his birthday on Wednesday. "It's costing me more to play my best tennis. It seems that it's costing me more to react, or recover. I play a good match and the next day I find it harder to react."
The Spaniard, whose ranking has fallen to No. 6, continues to play a full schedule, with seven events and one withdrawal so far.
His results include reaching the quarterfinals of the Australian Open and winning Buenos Aires for the third straight year. But he also had to retire in Acapulco with an abductor injury and subsequently missed Indian Wells. A year ago, Ferrer held a match point over Andy Murray before losing in the Miami final. This year, he failed to convert four match points in a fourth-round loss in Miami to Kei Nishikori.
Ferrer said he is not thinking of retiring, but would like the calendar changed in a way that allows younger players to play longer. "Tennis is much more physical, but the governing bodies have not changed anything," he said.