A lower back injury forced the American to miss the season-ending eight-man tournament starting in Shanghai on Sunday.
The ATP will meet with the breakaway tennis players' union to thrash out the future of the sport.
Defending champion Albert Costa narrowly escaped a humiliating French Open fate on Tuesday. A round-up of Day 2.
The 28-year-old hasn't recovered from an ankle tendon injury and will miss the Davis Cup quarter-final against Argentina.
Australia captain John Fitzgerald says Hewitt and Philippoussis are no guarantee that Australia will breeze through the Davis Cup match with an injury-racked British team.
Should Carlos Alcaraz win Queen's final against Alex de Minaur he would reclaim the world number one ranking from Novak Djokovic.
Indian pair of Leander Paes and Mahesh Bhupathi crashed out of men's tennis doubles event losing their quarterfinal match to Swiss duo of Roger Federer and Stanislas Wawrinka in the Beijing Olympics on Friday.
Former finalist David Nalbandian became the highest men's seed to perish at Wimbledon on Monday, beaten 6-4, 6-2, 6-4 by Canada's Frank Dancevic.
Maria Sharapova led a trio of Russians into the last 16 of the French Open on Saturday while a relieved fifth seed David Ferrer was given an unnerving reminder of just how effective Lleyton Hewitt's grit can be.
Australia could be in trouble for failing to field appropriate players in their two dead Davis Cup semi-final singles rubbers against Argentina in Buenos Aires on Sunday.
Wimbledon picks up the pace dramatically today with the fourth round of the men's and women's singles.
Ivan Ljubicic inspired Davis Cup champions Croatia to an unassailable 3-0 lead over Austria in the World Group first round.
Holders Croatia held a 2-0 lead over Austria after the opening singles in the Davis Cup World Group first round.
The move is designed to favour 2002 Wimbledon champion Lleyton Hewitt and this year's runner-up Mark Philippoussis.
Roger Federer raced to a 6-1, 6-4 victory over American James Blake to win the Cincinnati Masters.
Spaniard Nicolas Almagro took the world No 1 to three sets at the Cincinnati Masters.
Both reached the semi-finals of the Montreal Masters, beating Lleyton Hewitt and Frank Dancevic respectively.
Agassi remains top of the 12-month rankings with 4,090 points followed by Ferrero and Federer.
The American is quoted at 11-4 with compatriot Andre Agassi second favourite on 100-30.
The 1996 Wimbledon champions has been bothered by long-standing elbow injury.
The Argentine concluded an ideal warm-up for the French Open with a 7-6, 6-0 win over the Frenchman in the Poertschach International final.
Monfils, a wild-card entry at the Austrian event, will next face fourth seed Lleyton Hewitt after the Australian demolished Argentina's Diego Hartfield 6-2 6-2.
World number one Roger Federer suffered a stunning 7-5, 6-2 upset defeat by Argentine Guillermo Canas in the Pacific Life Open second round on Sunday.
Gonzalez reached the quarter-finals at Melbourne Park for the first time in seven attempts.
The two players were named as the top seeds for the men's and women's singles event at the Australian Open which starts on Monday.
A factbox on Roger Federer, who won his first U.S. Open title with a 6-0, 7-6, 6-0 victory over Australian Lleyton Hewitt.
Roger Federer's free-flowing tennis must blast its way though solid rock when he clashes with Lleyton Hewitt.
The French Open champion had to retire from his Stella Artois quarter-final against Australian Lleyton Hewitt with a shoulder injury.
Rafael Nadal will face Robin Soderling in the first round with a likely fourth round clash against Lleyton Hewitt
Holders Croatia had to be content with a win and a loss from the opening day's two singles rubbers in the Davis Cup.
On a day of upsets at the Pacific Life Open, Australian Open runner-up Marcos Baghdatis beat 7th seed Gaston Gaudio.