Dustin Johnson is hoping to kickstart a big year by defending his title at the Saudi International despite only playing in two events since the 2019 Tour Championship last August.

The former world number one American underwent arthroscopic surgery on his left knee in the first week of September and played only one tournament after that in 2019 when he was part of the US Presidents Cup team at Royal Melbourne.

The 35-year-old started his 2020 season in Hawaii at the Tournament of Champions and was tied seventh. Johnson has slipped to No.5 in the world ranking and takes on a strong field that includes world No.1 Brooks Koepka, 12th-ranked Patrick Reed, the reigning British Open champion Shane Lowry and five-time major champion Phil Mickelson at the Royal Greens Golf Club outside Jeddah.

Johnson said he was looking to step up from his performances in 2019. "Last season was okay," he said. "Definitely didn't play quite as well as I would have liked to, especially towards the end of the year. This year, I'm looking forward to having a big year. I feel like the game is in pretty good form. Obviously, I haven't played much since Atlanta but I had surgery in the off-season so I'm just kind of getting back into it. Everything feels really good, and I'm excited about this year.”

Johnson won the inaugural event last year with a two-stroke victory over the Chinese Li Haotong and is keen to repeat the victory. "Any time you've won somewhere, you're looking at defending it but every event that I go to, whether I've won there or not, I'm always trying to win it. Just because you won at a golf course, it doesn't mean you're going to win again. You're going to have to work for it.

"It's more like a process. Like I want to get myself in contention. I just want to give myself a chance to win on Sunday."

Koepka, who is also making a comeback from stem cell treatment in his left knee that kept him away from competitions for more than three months, was impressed with the way the golf course had matured in a year since the inaugural edition.

Following his appearance in the Abu Dhabi Championship, where he finished tied 34th at eight-under par, Koepka spent the last week in Dubai practicing before his trip to Saudi. "Just practiced all week. I had three months off so there was no point in having a holiday or a vacation," said the four-time major champion. "It was more of a work thing. Just got the game ready. Felt good in Abu Dhabi. Felt good in Dubai. And I am feeling good here.

"It's just a matter of going out and executing. I played just fine and hit some great shots in Abu Dhabi. Just didn't score and that's my own fault. Just coming here to try to figure it out and put some scores together and try to eliminate some mistakes."

The $3.5 million tournament starts Thursday.