TENNIS AUSTRALIAN OPEN:RAFAEL NADAL last night refused to disclose the nature of the problem which ended his hopes of landing the "Rafa Slam" at the Australian Open, but accepted such injuries were "part of the sport".

The Spaniard appeared to strain his left hamstring in just the second game of his quarter-final against David Ferrer and was powerless to prevent his countryman from cruising to a 6-4 6-2 6-3 win and a last-four spot against Andy Murray.

Nadal would not answer specific questions on the subject, partly out of respect to Ferrer, partly because he claimed he did not know the exact nature of the injury and partly because he did not want to be portrayed as making excuses.

But it all adds up to a miserable start to 2011 for him after he also contracted a virus which saw him lose in the semi-finals of the Qatar Open at the start of the month.

He said: “I cannot say anything about the injury. I would prefer not to talk about it.

“First of all, I don’t know anything and secondly, for respect for the winner and a friend, I would prefer to talk about the match.

“It is obvious that I didn’t feel my best and had a problem during the match at the very beginning.

“After that the match was almost over. It’s difficult to come here and speak about it. In Doha I wasn’t healthy and today I have another problem. It seems like I always have a problem when I lose and I don’t want to have that image.”

The world number one had to pull out of his quarter-final against Murray 12 months ago to the day with a knee problem when two sets down before going on to win the French Open, Wimbledon and US Open.

He arrived in Melbourne aiming to become the first man since Rod Laver in 1969 to hold all four major titles simultaneously.

And he conceded he was bitterly disappointed at being denied a crack at history. “It is a difficult day for me but I tried my best and couldn’t do any more,” he added.

A problem with Nadal’s leg became apparent when he left the court at 2-1 down in the first set for a medical time-out. When he returned with his hamstring heavily strapped, a shake of the head in the direction of his camp further suggested he would not be able to produce his customary all-action style.

And so it proved as Ferrer, to his credit, played the perfect game, moving Nadal around and taking the chances which came his way.

Nadal was hindered further when the match was stopped for 10 minutes so the players would not be distracted by the nearby fireworks to celebrate Australia Day.

The period of inactivity halted the top seed just as he seemed to be warming to the task and the match quickly petered out. Afterwards, Ferrer admitted it was not the way he wanted to go through.

“It’s not easy, Rafa is a gentleman and played on after being injured in the first set,” he said.“I played aggressively and tried to go to the net but if Rafael was not injured I would not have won in three sets. It is a win but not how I wanted to win.”

Kim Clijsters remains favourite to win her first Australian Open after beating Poland’s Agnieszka Radwanska 6-3 7-6 although Russia’s Vera Zvonareva, hunting a first major, will provide a tough semi-final opponent after she beat Petra Kvitova 6-2 6-4.

In the absence of injured 2010 champion Serena Williams, Clijsters is the woman to beat in Melbourne.

The 27-year-old Belgian’s game was far from perfect but she hustled and bustled her way through the opening set in less than half an hour and fended off a Radwanska fightback to secure the second, and the match, in a tiebreak.

“I just physically felt a little bit tired and heavy out there today,” Clijsters said.

The three-times US Open champion will probably have to raise her game for the semi-final against Zvonareva, who wore a black ribbon on her visor in memory of the victims of Monday’s bombing at Moscow airport in her victory over Czech Kvitova.

An aggressive Zvonareva clipped through the first set in 29 minutes and was 3-0 up in the second when she also had a second-set wobble before battling back to go through a comfortable winner when Kvitova overcooked a forehand after 75 minutes. “There will be moments where you lose your focus and you will have one or two unforced errors,” said Zvonareva, a tearful losing finalist at Wimbledon and the US Open last year.

“But I’m really happy the way I handled the situation after, and I was able to come up with some good shots when I needed it and finish in two sets.”