Belgium’s David Goffin will contest Novak Djokovic’s final round-robin match at the World Tour Finals on Thursday after Gael Monfils withdrew.
Monfils, who had been eliminated anyway, has struggled after hurting his ribs in Stockholm in October.
“I tried to make it, but I couldn’t,” said Monfils, who has lost to Dominic Thiem and Milos Raonic at the O2.
Djokovic, who is already into the semi-finals, can earn 200 ranking points by beating first alternate Goffin.
The Serb is attempting to win a fifth straight World Tour Finals – a result which would ensure he reclaims the world number one spot from Britain’s Andy Murray.
Murray leapfrogged Djokovic to reach the top of the rankings for the first time in his career on 7 November.
World number 11 Goffin, 25, has lost all four of his previous meetings with Djokovic – most recently in the semi-finals of the Miami Masters in March.
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Great Britain’s Davis Cup first-round tie in Canada will be held in Ottawa’s TD Place Arena from 3-5 February.
After winning the title for the first time since 1936 in November 2015, Great Britain’s defence ended in semi-final defeat by Argentina in September.
Britain’s Andy Murray could face world number three Milos Raonic in a repeat of his Wimbledon win earlier this year.
Defeat for Great Britain would mean they have to contest a play-off to remain in the elite-level World Group.
The match will be played on an indoor hard court with capacity expected to be about 8,000.
Watch five of the best shots as Andy Murray beats Kei Nishikori in a thrilling encounter at the ATP World Tour Finals in London.
Andy Murray fought back to beat Kei Nishikori in a gruelling contest and close in on a semi-final place at the ATP World Tour Finals.
The world number one lost a tie-break but came through 6-7 (9-11) 6-4 6-4 against the Japanese fifth seed.
At three hours and 20 minutes, it was the longest match at the event since it moved to London in 2009.
Murray, 29, will qualify for the last four if Marin Cilic beats Stan Wawrinka in the evening session at 20:00 GMT.
It is the first time since his debut in 2008 that the Briton has won his opening two group matches.
The victory, his 21st in succession, had added significance as Murray needs to at least match Novak Djokovic’s results in London if he is to stay ahead of the Serb in the year-end rankings.
Djokovic has a 2-0 record in the Ivan Lendl Group, as does the Scot in the John McEnroe Group, having beaten Cilic in his first match.
It was resilience rather than brilliance that eventually carried Murray through in a match that lasted eight minutes longer than his 2010 semi-final loss against Rafael Nadal.
The Wimbledon champion erased the memory of his US Open quarter-final defeat by Nishikori in the most punishing manner.
“I feel OK right now, but it is the following day when you feel it often,” said Murray.
“Hopefully there will be another three days to this season and I’ll do my best to get through them.”
Nishikori, 26, deservedly took the opening set but only after an 85-minute tussle that saw both men create – and miss – numerous opportunities.
Murray netted a forehand on set point before they headed into a remarkable tie-break, which saw the Scot recover from 6-3 down – saving the third set point with an outrageous backhand when all seemed lost.
Nishikori fended off two more set points, one with a spectacular smash, before converting his fifth chance when Murray found the tramlines.
The 16,000 spectators buzzed with excitement but there were signs that the players were understandably flagging as the match wore on.
Murray could not hold on to an early break in the second set, with Nishikori breaking serve for the first time after two hours to make it 4-4, but the Briton toiled his way through the next two games to level.
A net cord helped Murray get the crucial first break at 2-1 in the deciding set, but even with a 5-1 lead there were more twists to come.
Nishikori discovered a burst of energy to peg Murray back to 5-4, but the top seed found his range when he needed it to serve out the match at the second time of asking.
“I eventually got over the line,” added Murray. “These are the sort of matches you work so hard for.”
| John McEnroe Group | ||||||
|---|---|---|---|---|---|---|
| Played | Won | Lost | Sets won | Sets lost | Points | |
| 1. Andy Murray | 2 | 2 | 0 | 4 | 1 | 4 |
| 2. Kei Nishikori | 2 | 1 | 1 | 3 | 2 | 2 |
| 3. Stan Wawrinka | 1 | 0 | 1 | 0 | 2 | 0 |
| 4. Marin Cilic | 1 | 0 | 1 | 0 | 2 | 0 |
After both suffered straight sets losses on Monday, Stan Wawrinka and Marin Cilic will need to show major improvements…
Andy Murray and Kei Nishikori face off on Wednesday afternoon with the winner confirming their progress from the…