Johnson forced out of Masters

World number 12 Dustin Johnson is out of this week's Masters because of a back injury.

With no reserves for the opening major of the season, Johnson's withdrawal reduces the field from 97 to 96 players.

It comes only a day after he told his followers on Twitter: "Oh yeah ... it's MASTERS week!!!!". In his next message, however, he said: "First I have to apologise to the fans and sponsors. With heartfelt regret, I won't be playing in the Masters due to a tweaked back."

He continued: "You have no idea how much I wanted to walk the fairways at Augusta and fulfil what I've been practicing for!! I'll have to root my buddies!"

The five-time PGA Tour winner underwent off-season knee surgery immediately after the Presidents Cup in November.

His last tournament was the WGC-Cadillac Championship at Doral four weeks ago. He tied for 35th place.

Johnson has played three Masters, with a best finish of 30th on his 2009 debut.