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.
Johnson won the Genesis Open in February to reach world number one and then added victories in the WGC-Mexico Championship and WGC-Dell Technologies Match Play.
The 32-year-old has also finished sixth and fourth in his last two Masters appearances, but was taking nothing for granted in his pre-tournament press conference on Tuesday.
"I mean, golf, it's a funny game," the US Open champion said. "It doesn't matter how good you're playing, you can still not win. Same goes for this week.
"If I want to win here, everything's going to have to go well for me. I'm going to have to drive it well, hit my irons well, putt it well. Everything is going to have to be really good.
"I've got a lot of confidence in my game right now, especially with the way I've been playing the last few tournaments. But, you know, anything can happen."