Paris - Novak Djokovic on Tuesday added his voice to calls for a re-think of the late-season ATP calendar, admitting that he is having to work hard to hold up physically through this week's Paris Masters to the year-ender in London.
The Serb, who will finish the season as world No 1 for the second year running, said he is trying to conserve his strength for the final competitive sprint - even in a season shortened by a fortnight.
"It is a big challenge," he told a news conference in the French capital.
"Obviously I'm sure all the participants in London will agree that this (ending the pre-London preparation week) is definitely not something that goes in the favour of us preparing for the most important event in the end of the year."
The last two spots in the World Tour Finals will be decided during play this week.
Djokovic himself has not played since beating Britain's Andy Murray for the title in Shanghai this month, then resting for two weeks.
While Djokovic and Murray are competing in Paris, current world No 1 Roger Federer is not, with the Swiss taking a break before the start of the eight-man World Tour Finals on Monday.
Djokovic, whose own health (possible stomach virus) and that of his father, who is reportedly ill in a Belgrade hospital, have been the subject of speculation in recent days, said nothing on either matter.
Instead, he indicated that he feels wiped out after a long season during which he and his team have tried to conserve strength for the run-in.
"This is the schedule. It is the way it is. We have to adjust, we have to accept it," he said. "Unfortunately, there is no other options at this moment.
"But we will discuss this matter after we finish this season. Maybe we can try to find some other way.
"This season is shorter by two weeks. Now we have a two weeks longer off-season. Maybe that was the sacrifice we had to make.
"There are still some options on the table about this (pre-London) week. Maybe we can move it around so we can make it more adjustable for the top players."
Djokovic added: "Physically I feel good now, but I'm not the freshest guy on the Tour because I have had a long year. But I want to try to hold on these two weeks and perform my best, and then go to holidays."
On court, France's men continued to impress in front of the home public, with two more advancing into the second round.
Wildcard Paul-Henri Mathieu, who missed 2011 with a knee injury, came through in dramatic style over Spanish qualifier Robert Bautista-Agut 6-4, 7-5.
The world No 64, who played a Basel semi-final at the weekend, was broken while serving for the match in a game which lasted an incredible 27 minutes and featured 15 deuces and 12 break points.
Bautista-Agut finally won it for five-all only to lose serve again as Mathieu squeezed through into a match with third-seed Murray.
Compatriot Jeremy Chardy set up a match with Canadian Milos Raonic as he defeated Guillermo Garcia-Lopez of Spain 6-0, 6-3 while Bulgarian Grigor Dimitrov beat Austrian Jurgen Melzer 7-6 (7/2), 6-2.
Polish qualifier Jerzy Janowicz reached the first of the third-round spots as he upset Croatian 13th seed Marin Cilic by the same scoreline.
Latest results from the second day of the ATP Paris Masters on Tuesday (x denotes seeding):
Paul-Henri Mathieu (FRA) bt Roberto Bautista (ESP) 6-4, 7-5
Jeremy Chardy (FRA) bt Guillermo Garcia-Lopez (ESP) 6-0, 6-3
Grigor Dimitrov (BUL) bt Jurgen Melzer (AUT) 7-6 (7/2), 6-2
Igor Sijsling (NED) bt Oleksandr Dolgopolov Jr. (UKR) 6-4, 6-2
Jerzy Janowicz (POL) bt Marin Cilic (CRO x13) 7-6 (8/6), 6-2