Andy Murray arrived at the Australian Open in the form of his life. Unbeaten, the world No4 was the bookies' favourite to win a first Grand Slam and his closest rivals were very publicly irritated by this unprecedented attention for a British player away from Wimbledon.

Having retained his Doha title a week before the Open, Murray looked and sounded like the real deal which makes his fourth-round loss to Fernando Verdasco even tougher to take.

While the Scot refused to blame recent illness for his 2-6, 6-1, 1-6, 6-3, 6-4 defeat the evidence of poor health was there for all to see in the form of a cold sore at the side of his mouth.

To battle it out with the Spanish left-hander for three hours and 12 minutes when less than fully fit was a brave effort by Murray but it could damage his tennis in the coming weeks.

Murray built up wonderful momentum with those 11 successive wins in 2009 and was playing with a freedom and potency that not even Rafael Nadal or Roger Federer, the world's top two, could deal with.

Now, he will turn up for his next tournament in Rotterdam on 9 February as the highest seed ejected from the Australian Open before the quarter-finals and with this month's unbeaten run firmly consigned to the record books.

For Murray, the big question is: has he hit the buffers or merely taken a minor detour on the way to a first Grand Slam title?

Patently, one defeat — against the world No14 — is hardly a crisis for Murray but he knows his coach and trainers need to instigate a clinical dissection of why he came up short here.

He said: “I will speak to my coach, the guys that I work with, and see if there's things that I could have done better, things that I can improve.

“For me, it's not a disaster. I'm still playing well and I lost to a good player in a very close match. I will have more chances to win Grand Slams.”

It is important Team Murray now examine how much work the 21-year-old did during a very testing three weeks training in Miami in December, which saw him put on an extra six pounds of muscle while undertaking lung-busting 400metre repetition runs on the track.

Murray spent Christmas at home before appearing in the lucrative Abu Dhabi exhibition event and then successfully defended his Doha title before finishing his Open preparations with a week practising on the baking hot Melbourne courts.

Did Murray's physical exertions make him susceptible to the flu-like virus that undermined his cause today? Was it the same problem that earlier left 13th seed Victoria Azarenko staggering around the baseline before defaulting against Serena Williams?

If Murray was left open to infection, then coach Miles Maclagen and the fitness guys will have to seriously consider amending the amount of work they ask Murray to do in what is a ridiculously short break between seasons.

Health issues apart, Murray has improved his first-serve percentage, ground-stroke power and willingness to come to the net, however, there are still areas of his game that need upgrading if the British No1 is to end our 73- year wait for a men's Slam champion.

The Murray second serve can be exposed by the top players and he needs to improve the depth, variation and pace of that key part of his game while the drop shot continues to infuriate regular watchers of the Scot.

When Murray is on song it is a weapon of mass distraction, driving opponents mad with its disguise and side spin.

However, when he is trying to pick up cheap points in a match that's in the balance, his quality control button goes awry. Poorly-executed drop shots deliver cheap points to an opponent who is lifted by the sight of Murray reverting to his comfort-blanket shot.

Ironically, he had been using the shot with better judgement this year, yet when he was under severe pressure against Verdasco the old problems arose. Critically, he delivered an awful drop shot when a point away from breaking serve at the start of the final set and then compounded the error by losing the first point of the next game with another howler.

Another old failing which emerged again was a lack of discipline as the British No1 lost his cool. In the fourth set he berated himself with a cry of “what the hell are you doing?” and was then lucky to avoid any action from the umpire when he swore loudly.

Murray's mood was much better early in the match as Verdasco was unable to dictate any of the rallies.

After 35 minutes of largely untroubled tennis and just seven unforced errors Murray was one set up but Verdasco's powerful forehand started to have a big effect in the start of the second set as he raced into a 4-0 lead.

The Spaniard closed that out 6-1 but was then broken in the second game of the third set, which Murray went on to win convincingly.

Murray then lost all momentum, and his serve, at the start of the fourth while the final-set shoot-out went with serve until the seventh game, when Verdasco appeared to dig deep and find energy reserves which an increasingly dejected Murray simply didn't have.

From 4-3 up, Verdasco just had to hang on to his serve, which he did to set up three match points at 40-0 up in the final game. While Murray saved the first and then the second, a shot into the net was enough to give Verdasco the win and end British hopes of a Grand Slam winner — at least until Paris in late May.

But providing Murray can sort out the remaining problems in his game and ensures his body can fight off illness at key points of the year, then he will achieve that Grand Slam dream.