British No 1 Andy Murray has slipped out of the world’s top 10 for the first time since 2008, following Marin Cilic’s victory at the US Open.
His ranking of 11 means he faces a battle to secure one of the eight slots available for the end-of-season World Tour Finals in London in November.
Murray has a significant number of points to make up on Tomas Berdych, who occupies the final qualifying position. The 27-year-old lost to Novak Djokovic in the quarter-finals in New York.
The Scot is due to play three more events before the London tournament and he may need to reach the final of either the Shanghai or Paris Masters to have a decent chance of qualifying.
Murray has fallen from three to 11 in the rankings since having back surgery in September 2013, two months after winning Wimbledon.
Since his operation, he had not beaten a top 10 player until overcoming Jo-Wilfried Tsonga in round four at Flushing Meadows.
At the other three majors in 2014, Murray reached the last eight at the Australian Open and Wimbledon, while he was beaten at the semi-final stage of the French Open.
Cilic struggled to comprehend his sudden elevation to become tennis’s newest grand slam champion.
The 25-year-old arrived in New York as a player who had never challenged for any of the sport’s biggest prizes, but leaves as US Open champion.
Cilic overwhelmed his fellow surprise finalist Kei Nishikori 6-3 6-3 6-3, carrying the momentum from his stunning semi-final victory over Roger Federer and turning it into major silverware and a cheque for $3m.
The Croatian said: “It seems completely unreal to be called a grand slam champion. I was dreaming about this all my life and suddenly the last four or five days everything started to change. And with my tennis especially. I started to play absolutely unbelievable, starting with the fifth set with (Gilles) Simon. After that I had an unbelievable run of matches against these top guys.
“It means everything. It’s just a huge accomplishment and a huge moment for myself and for my team and for everybody around me who was with me all these years supporting me, believing in me and never giving up. So this is just the peak of the world.”
Cilic is the first Croatian slam champion since Goran Ivanisevic.