Novak Djokovic won his third consecutive ATP World Tour title after Roger Federer dropped out before the finals because of a back injury.
33-year-old Federer, who who has won the tournament six times, confirmed his exit after the doubles presentation ceremony on Sunday, the BBC reports.
“I tried everything I could last night and today — painkillers, rest — until the very end, but I can’t compete at this level with Novak,” he said at the O2 Arena. “In a final like this and at my age, it would be too risky. I hope you understand.”
On Saturday Federer defeated Stan Wawrinka in the semifinal match, though he began showing signs of the injury toward the end. He later did not show up for a scheduled Sunday practice.