World number one Andy Murray has admitted that he cannot afford to drop his performance levels when taking on Milos Raonic in the semi-finals of the ATP World Tour Finals on Saturday afternoon.

The 29-year-old made it into the knockout stages of the end-of-season competition by winning all three of his round-robin ties, including an emphatic straight-sets win over Stanislas Wawrinka in his last outing.

Standing between Murray and a place in the final, where he could face off against Novak Djokovic - the man he ousted as the world's top-ranked player last weekend - is a meeting with Raonic, who he has defeated in eight of their 11 previous matches.

Despite his impressive record against the Canadian, which includes victories in each of the last seven, Murray believes that he could be in for a tough afternoon due to his opponent's powerful serve.

"He obviously serves big and goes for his shots. He moves forward when he has the chance. I think he probably likes the conditions here. It's a little bit quicker," he is quoted as saying by Sky Sports News. "You don't normally get loads of opportunities against the big servers.

"Then it comes down to, when you do get those chances, whether you take them or not. This year, when I have played him I have created a few opportunities in the matches. When they have come, I have been pretty clinical. I will need to be the same tomorrow if I want to win."

Djokovic will face Kei Nishikori in the other semi-final showdown, with the final scheduled to take place at London's O2 Arena on Sunday evening.