LONDON—Milos Raonic, who pulled out of his final round-robin match against Kei Nishikori at the ATP World Tour Finals, says his leg injury could be significant. The Canadian said he became hurt when he was playing against Andy Murray on Tuesday, a match Raonic lost 6-3, 7-5.

“Through extensive sort of research with the doctor's team here, we found that I have a slight tear on the vastus medialis on my quad,” Raonic said. “Just a large area of swelling, about five centimeters long, three centimeters wide, and one centimeter deep of swelling and bleeding.”

Raonic said he thought that he was cramping against Murray, and that it did not affect him. However, he was not able to run as fast as he could.

The world No. 8 says that pulling out of the exclusive tournament was the right move. He did not want the injury to get any worse and potentially lose training time during the off-season in November and December.

“If I was to step out on court, I'd sort of be walking a tightrope where I can play obviously not at 100 percent, but with a significant risk of losing up to six to eight weeks if things go badly,” he said.

“So losing six to eight weeks of solely rehab, sort of means you lose 12 weeks of getting back into shape and everything, those are definitely significant factors in my decision. At some points I didn't want to accept it and listen to it. But it is what it is. I, alongside my team, all the staff with the ATP, made the best decision I believe.”