World number one Dustin Johnson is a serious doubt for the Masters after injuring his back in a "serious fall" on Wednesday, his agent has said.

Johnson, who has won his last three events and was favourite to win a second major title at Augusta National, suffered the fall in his rented house.

"At roughly 3pm today, Dustin took a serious fall on a staircase in his Augusta rental home," his agent David 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."

Johnson does at least have the advantage of being in the final group out on Thursday at 2:03pm local time.