Lionel Messi says Argentina's match against Australia will be 'very difficult'

One of greatest football players to ever grace the face of the earth is fearful of Australia – well, sort of.

Lionel Messi admits Argentina's Round of 16 clash against the Socceroos will be 'very difficult'.

Anyone else sensing a bit of worry in Messi's voice?

From World Cups to Champions League finals, the great man has played in some of the biggest games football has to offer.

So, to put it simply, he knows a tough test when he sees one.

Enter, Australia.

A certain someone has clearly been keeping a close eye on the lads in green and gold as they registered two wins to finish second in Group D on the same points as France.

And, well, let's just say he's not taking them too lightly.

"The match against Australia is going to be very difficult," Messi said following Argentina's 2-0 victory over Poland.

"Anyone can beat anyone, it's all even. We have to prepare for the game as we always do."

Yes, granted, Messi is probably being the consummate professional he is by encouraging his team to not take their foot off the gas.

But for a Socceroos side that was widely written off before they'd even touched down in Qatar, to have a footballing icon make these sort of comments is nothing short of special.

Speaking straight after the final whistle, Australian coach Graham Arnold immediately turned his attention to the colossal task at hand.

“No celebrations,” he said on SBS' broadcast.

“As I said to the boys, that’s why we won after a great win against Tunisia.

“No celebrations, no emotion. Sleep. No social media.”

While Arnold is now clearly focused on Messi and Co, he did recognise his side's monumental effort to come out on top against Denmark.

“Just so proud of the effort by the boys,” Arnold added.

“Short turnaround but their effort was incredible.

“[It took] a lot of belief, a lot of hard work. These boys come in with a great mindset. We’ve been working on this for four and a half years. We have the belief, the energy and the focus.

“I could see in their eyes that they were ready tonight.”