* 'It sucks really bad' says Johnson
* Back injury restricts swing
* Worked all night to get ready (Adds quotes, detail)
AUGUSTA, Georgia, April 6 (Reuters) - World number one Dustin Johnson pulled out of the U.S. Masters on Thursday after sustaining a back injury in a freak fall, leaving the year's first major without the red hot favourite.
The American, heavily fancied to win the title after victories in his last three tournaments, slipped on stairs in his rental house on Wednesday sparking immediate speculation he would not be able to play.
"I just don't feel like there is any chance of me competing," Johnson told a crowd of reporters outside the clubhouse. "It hurts.
"I was doing everything I could to try to compete. I was up all night trying to get ready for today.
“I can't make my normal swing and I just don't feel like there is any chance I can compete.
"Obviously I want to play more than anything. I just can't swing the club.
"It sucks. I am playing maybe best golf of my career and this is one of my favourite tournaments.
"It sucks, it sucks really bad."
Johnson had arrived at Augusta National around noon and warmed up under the watchful eye of swing coach Butch Harmon.
The situation appeared dire as the 32-year-old took a few cautious swings.
The big-hitting American was in clear discomfort, unable to bend over and leaving his caddie to tee up his ball.
As his 2:03 p.m. tee time approached, Johnson was in deep discussion with his team on the range but seemed determined to play telling a television reporter he was going to give it a try.
A grim-faced Johnson made his way to the first tee but after a few swings turned and walked to the clubhouse.
It was later announced he was withdrawing from the tournament.
Johnson shed some light on the series of events that led to the injury, explaining that he was coming downstairs in socks to move the car when he slipped falling hard on his back and elbow.
"I was doing everything I could to try and play," said Johnson. "Last night, ice, heat, ice. I was up pretty much all night trying to get it ready for today.
"Worked on it all morning. I can't make my normal swings and I don't feel there is any chance that I could compete.
"Obviously I want to play more than anything but just sitting there on the putting green ... I just can’t swing the club." (Editing by Ed Osmond, Louise Ireland and Andrew Both)