Hamstrings and T20 maths on Finch's mind

Aaron Finch says maths was never his strong suit at school.

But he reckons in a cricket sense, he goes OK with numbers.

"Not bad when it's in cricket terms," he said.

"Anything else - maths wasn't my best subject at school."

Maths and hamstrings will dominate the Australian captain's thoughts on Friday before the must-win T20 World Cup clash against Afghanistan.

Finch and power-hitter Tim David are both battling to overcome hamstring strains in time to play against the Afghans at Adelaide Oval.

"If I don't feel confident in my hamstring ... if I feel any pain or anything like that, I won't play," Finch said on the eve of the match.

David was in "exactly the same boat", the skipper said.

"You don't want to compromise the team performance by having a guy go down who comes in with a niggle," Finch said.

The fitness clouds hover as Australia face the moment of truth in their T20 cup defence - lose to the Afghans and the dream is over.

Win, and it still might not be enough to advance to the semi-finals.

Australia are third in their group behind England and leaders New Zealand, with all three nations on five points.

The Kiwis play Ireland in Adelaide on Friday afternoon before Australia's game, while England meet Sri Lanka in the last game of the group on Saturday.

Should the three favoured nations win, net run-rate will decide the two who progress to the semi-finals.

Finch said there would be number-crunching, but not at the expense of losing focus on the primary goal: beating Afghanistan.

"We will go through all the scenarios to make sure that we're crossing our t's and dotting our i's and just so that we have got a clear mind on what we need to achieve," Finch said.

"First and foremost, we have got to try and get the two points (for a win)."