Andy Murray says he is taking nothing for granted ahead of his Australian Open quarter-final tie with Kei Nishikori, the fourth seed insisting he will need to be at his best to combat his opponent's new "power".

33988 - Andy Murray braced for transformed Nishikori

Since losing his first set of the tournament against Ryan Harrison, Murray has enjoyed a straightforward passage into the last eight, while Nishikori will enter the contest on the back of a five-set triumph over Jo-Wilfried Tsonga.

In theory, therefore, Murray should be the fresher of the two, but the Scot is aware of the work Nishikori has been doing in the gym and says the Japanese player's improved game demands respect.

"I have seen him in the gym a lot, especially in Brisbane the last few weeks," he said. "I think he has got himself in better shape, he is doing well."

"When I worked with Brad [Gilbert] and spoke to him about Kei, he said he needed to learn to love the gym. And, to be fair, I've seen him in there a lot doing good work.

"I think that can then help with your mentality on the court. Because he isn't as tall as some of the guys, getting stronger will have helped his game. He's playing very well."

Nishikori became the first Japanese male to reach the last eight at the Australian Open in 80 years after downing 2008 runner-up Tsonga 2-6 6-2 6-1 3-6 6-3 in three hours and 30 minutes, and Murray is well aware of the threat the world No. 26 poses.

"I saw a little bit of his match against Tsonga and he played really, really well," he said. "I have practised with him a few times and he's very good.

"He is very deceptive. For someone that's not the tallest he creates a lot of power from the back of the court. He deals with pace well, he can slice and he moves well. He was dictating all the points from the back of the court which is difficult against someone like Tsonga. He has also won a few long matches here."

Reflecting on his own form, Murray said he has plenty left in the tank and admitted standing nearer the baseline was an intentional change in tactic, conceived after discussions with new coach Ivan Lendl.

"I think the thing that has changed has been my court positioning," Murray told Eurosport.

"I haven't really changed the way I'm hitting the ball, I'm not hitting it much harder or serving much bigger. I'm just playing closer to the baseline, which means I can dictate more points and take time away from my opponent. By playing a metre closer to the baseline, your ball does a lot more damage down the other end."