ANDY Murray admitted last night that his chances at Wimbledon this year are being affected by a nagging injury to his right shoulder.

The Scot booked his place in the last 16 at SW19 for the ninth time with a 6-2, 6-2, 1-6, 6-1 winner against Andreas Seppi of Italy, in a match which saw both men call for assistance from the trainer Clay Sniteman of the USA, with his magic touch responsible for each man reeling off six game winning runs. While the World No 3 admitted the issue with his serving arm was not a major concern, he did say it had been dogging him for "two or three days".

"I only really feel it when I'm serving," said Murray. "It's not something that's of major concern to me, but obviously when you do take a break, it does stiffen up. And my serve was pretty bad after that happened. Once I had the treatment, I served much better, way harder. Just now, Clay, the physio, came on the court and said it was like a machine gun going off when he laid on top of me. My back cracked a lot."

Murray chastised himself for struggling psychologically to adjust to Seppi's initial injury time out, which saw him massaged on his lower leg. He surrendered the third set in quick time, then had to fight back from a break down in the fourth. "That's the psychological part of the game and maybe something I could have done a better job of dealing with," he said. "I was frustrated because I got broken, but also because my shoulder cooled down, and I started slowing down my serve."

Next up for the Scot, second on Centre Court on Monday, is the giant Croatian Ivo Karlovic. The 6ft 10in No 23 seed was a surprise winner against Jo-Wilfried Tsonga of France yesterday, and has now served 136 aces in three matches at SW19. "Obviously he has served extremely well this tournament," said Murray. "There were a couple matches here where he served over 40 aces. It's an extremely tough match. I'll need to be really sharp on my returns."