World No 1 Dustin Johnson says he will be seriously underprepared for next week's Masters after being sidelined due to coronavirus.

Johnson was confined to his hotel room for 11 days after a positive test for Covid-19 last month forced him to miss out on playing the CJ Cup in Las Vegas and the Zozo Championship in California.

The 36-year-old had finished in the top six in each of his previous five starts but now has just this week's Vivint Houston Open to get his game back in shape ahead of the year's final major at Augusta National, where he finished in a tie for second behind Tiger Woods last year.

"My health is good. The state of my game is undetermined," Johnson told a pre-tournament press conference at Memorial Park.

"It wasn't that bad (in) as far as I didn't get really sick. I felt like I had a cold for a few days and then after that I didn't - so I was pretty much asymptomatic.

"A little fatigue and things like that, but I couldn't really figure out if that was because I was stuck in a hotel room for like 11 days not doing anything or it was Covid that made me feel that way.

"I didn't leave the room for 11 days, I was just laying around kind of doing nothing. I watched a lot of TV, but even then I ran out of stuff to watch. It was really boring.

"It definitely puts a wrench in your plans on what you were trying to do. Obviously I was planning on playing Shadow Creek and Sherwood, those two events. I had a lot more time off than I was planning on."

Asked what he wanted to achieve this week, the former US Open champion added: "For me, it's just getting reps is all. If I hit a couple good shots, I'll be happy.

"Obviously I've had way more time off than I wanted coming into Augusta and so for me it's just kind of being out here and practicing and just getting some reps in because I definitely didn't plan on having this much time off."

Major champions Shane Lowry, Brooks Koepka, Danny Willett, Adam Scott, Sergio Garcia, Henrik Stenson, Phil Mickelson and Francesco Molinari are also in the field in Houston, along with BMW PGA Championship winner Tyrrell Hatton and Scotland's Martin Laird, who won the Shriners Hospitals for Children Open in Las Vegas last month.