Johnson is favourite to win the Masters title after victories in his last three tournaments.
"At roughly 3:00 pm today, Dustin took a serious fall on a staircase in his Augusta rental home," Winkle said in a statement.
"He landed very hard on his lower back and is now resting, although quite uncomfortably. He has been advised to remain immobile and begin a regimen of anti-inflammatory medication and icing, with the hope of being able to play tomorrow. I will refrain from commenting further until I know more about Dustin's condition."
The Masters starts in Augusta on Thursday with Johnson scheduled to play alongside fellow Americans Bubba Watson and Jimmy Walker in the last group out.
Read the original article on Eurosport: World number one Johnson doubtful for Masters after freak fall