Andy Murray admitted his ankle is "a little bit sore" after rolling it in his last Australian Open match but came through a practice session unscathed on Thursday.

The world number one's mood will surely have been raised by the shock exit of defending champion and rival Novak Djokovic, who went out in five sets to Denis Istomin.

The Serbian collapsed from two sets to one up against the world number 117 to crash out of the competition 7-6, 5-7, 2-6, 7-6, 6-4 and concede his Melbourne crown.

Speaking about the injury picked up in Wednesday's second round win over Andrey Rublev, Murray said: "It's just a bit sore today.

"I did roll it pretty badly [on Wednesday] but thankfully I can put weight on it and I was moving around fine in practice just now.

"It was just a little bit sore at the start and when I got up this morning but once I started moving around it felt all right."

Murray will face Sam Querrey in the third round on Friday, with the Scot expecting a challenge from the big serving American.

"The most important thing will be to serve well yourself because that then puts pressure on his service games," the Scot said.

"And then I'll just try to make as many returns as I can. Once I get in the rallies I should do okay.

"He can serve huge and if it's hot - I don't know what temperature it's supposed to be [on Friday] - but the conditions play quicker in the heat and that can make it even tougher to return the serve."