Rafael Nadal has resigned as vice president of the ATP Player Council, saying he can no longer give the job the attention it needs.
"I don't have enough energy," Nadal said on Tuesday. "I cannot still put in my 100 percent there."
Nadal pushed unsuccessfully for a two-year ranking system, a proposal opposed by other players, including council president Roger Federer.
Nadal and Federer were in agreement on other issues, arguing the major tournaments are too powerful and players need a stronger voice in decisions. Both were critical last year of the U.S. Open schedule.
Nadal, who has complained the tennis calendar puts too many demands on players, acknowledged there are unresolved issues.
"I am not frustrated," he said. But he added, "I believe that we can do much more things than what we have done. ... My feeling is a great opportunity to improve the sport, because today the players are very unified."
Nadal spoke after winning his fourth-round match at the Sony Ericsson Open.