Rafael Nadal gave proof of the agonisingly long ATP season as the top seed quit his Paris Masters quarter-final injured to join Roger Federer in pulling out on Friday.
Top seed Nadal, who has played more than 90 singles matches this season, received treatment on his right thigh and knee after the fifth game and gave up against Nikolay Davydenko after losing the first set 6-1, dpa reported.
Federer had pulled an hour earlier with a back injury, failing to take to the court against James Blake and calling the move a precaution for the Masters Cup in Shanghai which begins a week from Sunday.
The remaining two quarter-final matches were completed on a day of drama, with defending champion David Nalbandian produced a 7-6 (7-3), 6-3 victory to end the winning streak of Andy Murray at 14 matches.
Nalbandian faces Davydenko while Australian Open finalist Jo-Wilfried Tsonga thrilled French home crowd as he beat Andy Roddick 5-7, 6-4, 7-6 (7-5).
The victory took well over two and a half hours, with Tsonga saving all but three of the 17 break points he faced from the Roddick attack in mach of 29 aces.
The Frenchman will face Blake for the first time.
Federer said a back injury denied him the chance to play his match against Blake, who beat him in the Beijing Olympics.
"Usually overnight and maybe with painkillers you sort of get over it, but I just feel like I just can't play the way it is right now," the Swiss explained.
"I mean, you can hit balls, you can't play professional tennis against the best in the world.
"I hope I'll be fit again for Shanghai. This is a precaution for Shanghai. I hope I'll be okay in a couple of days.
"Usually, the back is something that takes a few days and it's better again. I've had a lot of back pain over all the years playing tennis, so it's not like the first time."
The decision puts extra pressure on Federer with the end-of-season event starting a week from Sunday. Federer, defending that title, is due to fly to China early next week.
The rare injury marked the first time Federer has withdrawn before a match. He has advanced at the expense of injured opponents 16 times dating to 2002 in Rotterdam.
"This is the first time ever I've pulled out during a tournament, so it feels bad," said the Swiss. "I don't like to do it. I hope I get well soon, so that's really it."
The unhappy ending will mean that for the first time since 2003, Federer has failed to win at least one Masters Series title.
Nalbandian took over provisional 11th in the chase to China with just two days to go in the sprint for the final two spots.
But the Argentine has said he is not certain to take part, preferring to save himself for the Davis Cup final against Spain in Mar del Plate November 21-23.
Murray had not lost since dropping the US Open final to Federer on September 8.
He and Federer, plus Nadal, Novak Djokovic, Davydenko and Roddick are already booked into the season-ending field.