Marsh joined a group of Australia's squad members, who are not involved in the IPL, for the first of two three-day pre-tournament training camps in Brisbane over the next two weeks before the squad heads to the Caribbean on May 25.

Marsh was initially not expected to travel to the first camp this week but his hamstring had improved enough for him to attend and bat in the nets over the past two days. But McDonald confirmed he would not be fit to bowl until much closer to the tournament.

"You probably won't see him bowl in the next couple of weeks here," McDonald told reporters at Allan Border Field on Tuesday. "It'll probably happen the week before we leave. And then he'll be able to ramp that up when we're over there. We'll be able to cherry-pick the moments during the tournament where he'll be useful with the ball. We've got some all-round depth in the squad, which gives us good coverage anyway.

"[His recovery was] probably a little slower than expected on the back of the hamstring. But we've got plenty of time now that he has been ruled out the IPL. The first game is just short of a month away now. So ample time for him to get ready. But really positive to see the skipper on the park."

McDonald said there was no concern around a lack of match practice for Marsh over the last two months given Australia will have some practice games before their opening clash with Oman.

"No real concern about match fitness," McDonald said. "We've got a couple of practice games when we get to Trinidad in the support period. So he'll likely get plenty of match opportunities. And if not, we'll be able to simulate those through practice, which our coaching staff are pretty good at."

Marsh, Josh Hazlewood, Josh Inglis, Ashton Agar and Adam Zampa are the only members of Australia's 15-member squad who are not currently at the IPL and all five were participants in the first two days of training in Brisbane along with Aaron Hardie, Tanveer Sangha, Matt Short, Matt Kuhnemann, Xavier Bartlett and Marnus Labuschagne. The latter is preparing to head to England for a county championship stint with Glamorgan and was the only player training with the red ball while the others are part of an extended group on standby as possible travelling reserves for the World Cup.

McDonald confirmed Australia would likely take one travelling reserve but they are yet to decide what type of player they need as cover for the 15-member squad.

"We've got some decisions to make," McDonald said. "We've seen some international sides have up to four reserves. That'll be something that [chair of selectors] George Bailey will get us together around in the next couple of weeks and we'll put the final touches on that squad. We will take a reserve at this stage and it's looking like one reserve."

McDonald was pressed on the age of Australia's squad after in-form youngster Jake Fraser-McGurk was left out of the squad. Australia will only have one player in their squad under the age of 28, with Cameron Green set to turn 25 just before the tournament starts. Nathan Ellis, Tim David and Inglis are the only other players in the squad under the age of 30.

But the coach backed his senior players to deliver again on the big stage.

"There's been a discussion around the age profile of our team in all formats," McDonald said. "I'm a big believer in you don't know when the end is going to be. And a lot of people write off those players just based around their age.

"We feel as though in the last 12 months in particular in the white-ball space we've given plenty of opportunities to other players. Have we gone back to the tried and tested in terms of World Cups and the performers that we know can perform on that stage? There's no doubt about that. It's players that have been there before and done it and are still in good form. And you look at David Warner in the last 15 games for Australia, his record is outstanding. Josh Hazlewood, Pat Cummins, Mitchell Starc, those players that are probably the elder statesman of the team are still performing at international level. And that goes a long way."