Jack Haig is another to watch among the nine Australian riders when the Tour starts on Friday night (AEST) with an individual time trial in Danish capital Copenhagen.

As 37-year-old Richie Porte nears retirement following his third place two years ago, O'Connor is the standard bearer for a new wave of Australian general classification hopefuls at the three-week Tour.

Australian cycling's Generation Now is also highlighted by Jai Hindley, who last month became the first rider from this country to win the Giro d'Italia.

But Hindley is yet to make his Tour debut and O'Connor's breakthrough fourth place last year confirmed he is the next big hope to join Cadel Evans as Australia's only Tour de France champions.

O'Connor joined Australian cycling luminaries Phil Anderson, Evans and Porte as top-five finishers at the Tour.

Now the question is, can the AG2R-Citroen leader climb onto the podium?

It will be a crowded queue - Slovenia's Tadej Pogacar (UAE Team Emirates) has won the last two Tours and is the overwhelming favourite.

Compatriot Primoz Roglic leads a powerful Jumbo-Visma squad that also features Danish contender Jonas Vingegaard.

Ineos Grenadiers have 2018 winner Geraint Thomas in their lineup.

O'Connor is keen to find out whether he has bridged the gap to the top favourites.

"At the start of the year, Tadej really did look untouchable, but it's difficult to tell because the start of the year is very different," O'Connor told AAP.

"Is he still like last year, where he towers above everyone and takes the piss, or are we now closer together, have we all improved?

"Do we know how much further ahead he is compared to everyone else?"

O'Connor showed strong form earlier this month at the Criterium du Dauphine stage race, finishing third overall behind Roglic and Vingegaard.

"Vingegaard, who was almost on the same level as Poggy at the end of last year's Tour, and Primoz took the race - but I was the closest to following and I wasn't far away," he noted.

"So when I think of this, then surely the gap can't be that much bigger."

Haig (Bahrain-Victorious) comes into overall calculations as well following his third overall last year at the Vuelta a Espana, the third of the Grand Tours after the Giro and Tour.

His Tour hopes were dashed last year when he crashed out in the hectic opening week.

The same fate befell Ewan, who needed surgery on a badly broken collarbone.

The sprint ace has won five Tour stages, but his team boss has spoken of "revenge" and Ewan is due.

He had a self-described "Giro from hell" last month, with no stage wins.

There will not be many opportunities for the sprinters in this year's Tour, but Porte says Ewan and Dutch fast man Fabio Jakobsen will be tough to beat.

"It was heartbreaking last year to see him on the ground," Porte said of Ewan's Tour crash.

"Caleb's tough - you know if Caleb's on the ground, there's something very wrong.

"He's almost indestructable.

"He and Fabio Jakobsen are probably the fastest guys in the world ... you get Caleb to the finish line, I don't think there's anyone who's going to get over the line quicker than him."

Australian Associated Press