Jason Day is sick of being sick.

The Australian former world No.1 is in California preparing for his 2021 debut next week at Torrey Pines, one of his most happy and fruitful hunting grounds.

Having watched his world ranking drift out as far as No.63 last year – the first time in more than a decade he’d been outside the top 50 – Day is desperate to use the Farmers Insurance Open as his springboard to make amends.

But rather than do it on what has been a sporadic, injury-affected basis as he has in the past couple of seasons on the PGA Tour, the Queenslander is in the process of rebuilding a healthy base.

A complicated rebuild of his swing with new coach Chris Como – the man who helped rebuild Tiger Woods’ swing after back fusion surgery – has Day confident that he’s found a method that will permit the 33-year-old to “play well into my 40s” without the pain that has dogged his past few American campaigns.

“Last year I was kind of coming over the top of (the ball) just to alleviate some of the back pain,” Day said today.

“My plan is to try and get more inside with the actual (swing) path, but if I do it straight away, it usually flares my back up.

“So I've just got to incrementally change my hips, my top position in regards to my back, my upper body, how that moves, and then hopefully overall just get the hips on the way through moving a little bit better to try and alleviate some of the pain.

“One of my goals this year is to try and stay healthy … and not use that as an excuse (when) things aren't going my way.

“It would be nice to put this in the rear-view mirror and not have to get on a (media) call like these and talk about my body and it breaking down.

“I've been talking about it for a long, long time now and … I'm trying to do the best job I can to make sure that I don't have to talk about it any more.”

Day, who will resume his 14th season on the PGA Tour with an assortment of manufacters’ clubs in his bag and no formal equipment contract, said he still believed he could return to No.1 in the world, a position he most recently held in February 2017.

“The biggest motivation for me right now is that where I'm ranked right now (No.43),” he said.

“I understand I'm there for a reason, but I know that I'm better than that.

“I know I can get back there. I feel like I have the game to do it. It's developing nicely, I've just got to stay healthy.”

Torrey Pines has been good to Day over the years. He won the world junior championship there and has been twice victorious and once runner-up in the Farmers Insurance Open in the past seven years.

He’s also got one eye on June this year when the US Open returns to the coastal San Diego layout where he knows length is at a premium.

He says he’s “excited” about the prospects of his tinkered swing, including the chance to edge his swing speed back to his zenith of 2016.

“I've got TrackMan data from the (2016) US Open where I was swinging 128 miles an hour club speed, and that was the longest that I've hit it. I was hitting it very long,” he said.

“Granted, I'm swinging at about 120 miles an hour right now, and I haven't done any training other than mobility, so I think once I get into the gym and I'm able to get obviously my mobility and flexibility back first, if I can do that, then I'm safe to train.

“Then I'll be able to get into the gym a little bit more and do more speed stuff, and if that's the case then I can probably add three to five miles an hour and try and get back. I probably won't get back to the peak of how far I was hitting it, but if I can get to 125-mile-an-hour club speed I'd be very, very happy with it.

“But sooner or later (with the old swing, my back) would just kind of flare up and go out.

“The thing that I'm working on right now, if I do it correctly, it doesn't hurt my back one bit at all.

“It may come and go, but I've just got to be really patient with it.”