While Chris Tremain laughs that he completely forgot he will be bowling to Australia's Test captain this weekend, he has vowed to never again let a golden opportunity escape his grasp.

Because, he admits, that's exactly what he did earlier this year.

The JLT Sheffield Shield's leading wicket-taker over the past three seasons, Tremain was enjoying a well-earned break back in May and was caught by surprise when he was summoned to join Australia's training squad ahead of their limited-overs tour of the United Kingdom.

After a punishing domestic season, the Victorian admits he was in far from peak physical condition.

When the call came he was on holiday in New Zealand, leaving him in a scramble to get himself right to impress new national coach Justin Langer.

Aside from earning back the trust of the Australian public after the ball-tampering saga, fitness has been the single biggest emphasis of the early days of Langer's tenure and Tremain concedes he was caught out.

"I'd come back from a holiday, I was a week into bowling and I got up to Brisbane and was half-cooked," the 27-year-old told cricket.com.au.

"I tried to train with the Aussies and I was – not shunned – but mollycoddled a bit because I wasn't ready to train and play with them."

When Josh Hazlewood was ruled out of the ODI series against England a few weeks later, Tremain wasn't considered for selection.

Michael Neser was picked as Hazlewood's replacement and, a few months later, Neser got the nod again for the Test squad to play Pakistan in the UAE after both he and Tremain had impressed on the Australia A tour of India.

Looking back, Tremain concedes the winter represents a missed opportunity.

"I never saw myself as a 12-month-a-year player," he said. "I saw myself as a seven-month player and then have a breather for six weeks and then go again.

"I got found out.

"I was like, 'alright, if I want to be at the top then I'm going to act like people at the top'. And they are constant, they're training and they are elite for 12 months of the year.

"It took me that kick in the guts (to realise) and I didn't actually get any feedback. I just believed that to be the case (that his fitness counted against him).

"I actually prefer it to be that case. I actually prefer to be disappointed about me not being ready because that is solely my responsibility.

"If I'm disappointed about that, then I'll make sure it doesn't happen again. And I don't believe I've missed an opportunity since."

A shot at impressing Test skipper Tim Paine in the days before the first Test squad of the home summer is due to be announced is the kind of chance Tremain, now in tip-top shape, won't let slip.

Having led all-comers on last season's Shield wicket tally, the right-armer has 17 wickets from Victoria's first three matches this season and again finds himself among the contenders to be picked as the fourth quick behind star trio Mitchell Starc, Pat Cummins and Josh Hazlewood this summer.

If some players claim they're giving national selection no thought when really they're being kept awake at night by the thought of it, Tremain isn't one of them.

When it was put to him on Friday that Victoria's upcoming Shield clash with Tasmania presents a perfect opportunity to impress Paine and push his case for higher honours, Tremain admitted his attention – and that of his teammates – had been centred on a different Tigers threat.

"I actually totally forgot 'Painey' was playing in this game because my entire focus was on how our top order is going to counter Jackson Bird," he said.

"I still think Jackson Bird is one of the best bowlers in the country at the moment. I've not really thought about Painey at all, it was more about their bowler and leader in 'Birdy'."

But in the back of his mind, Tremain is fully aware of how big this Shield round is.

Queensland's trio of Marnus Labuschagne, Matthew Renshaw and Joe Burns have the chance to enhance their Test prospects against the star NSW quartet of Starc, Cummins, Hazlewood and Nathan Lyon in their match in Canberra.

Travis Head and the Marsh brothers are also in action in the SA-WA clash at Adelaide Oval, while limited-overs captain Aaron Finch and his injured opening partner Usman Khawaja are the only incumbent Test players not featuring in this round of games.

"For outsiders looking in, Shield cricket becomes more exciting and more exotic when these guys are back," said Tremain.

"I recall a game where we played NSW at the SCG (in 2016) and Pete Handscomb got 215 and worked his way into the Test squad. They had (Steve) Smith, (David) Warner and Lyon playing for them and we had this really good feeling that 'we want to beat these guys when they're at their strongest'. And we did.

"It's a great opportunity to take a bite out of the biggest apple you can find.

"A few years ago that was Smith and Warner, this week it's Tim Paine. For the Queensland guys, it's an opportunity to do it to the big three (fast bowlers) and Nathan Lyon.

"Not only is it great for outsiders looking in, but cricket in Australia is in a great spot at the moment. It's a great opportunity for players to beat their chest and go 'I can rumble with the best.'"