Three years ago, just after Roger Federer had broken Jimmy Connor's record of holding the world No 1 ranking for 161 consecutive weeks, John McEnroe claimed "current players are too respectful" of the Swiss.
"I think you need to attack him and put pressure on him," McEnroe said. People like Andy Murray and Rafael Nadal seem to have taken up that advice, and Federer, at the moment, is looking short of answers.
Nadal boasts a 14-7 record against Federer, which includes victories in five grand slam finals, while Murray has won eight of his 13 matches, the most recent being in the final of the Shanghai Open on Sunday.
After that win, Murray admitted he deliberately adopts an aggressive strategy against the 16-time grand slam winner. "I love the challenge of playing against him and I don't fear playing him," the Scot said.
Approaching 30, Federer's sublime gifts are definitely on the wane, but his diminishing aura - and the defeats against Nadal - have probably played a greater part in the Swiss maestro's meagre returns this season. He has won just two of the six finals he reached this year and only reached one grand slam final, to make it his poorest showing at the majors since 2003.
Can Federer reverse this decline? He definitely can, but he will probably need a few good wins against Nadal to get back to top spot, something that he has managed just once in the last seven duels.