Prior was set to train at full pelt at the Gabba as he battles to recover from the injury that kept him out of England’s final warm-up game in Sydney last week.
The Sussex star, who has played 57 consecutive Tests, came through another training session yesterday and flashed a thumbs-up in the direction of England team director Andy Flower.
But today’s final workout will ultimately determine whether he maintains that run of consecutive appearances or whether Bairstow will be catapulted back into the cauldron of cricket’s greatest rivalry.
In his newspaper column, Prior said he would have to be able to train at “100 per cent” today to convince the medical team and admitted the outcome was not a foregone conclusion.
“It will be touch and go whether I am fit in time,” he wrote.
“I’m optimistic I will be okay, but it is a long series and as much as you want to play in the first Test, I do not want to come back too early, tear it again and be out for a long time.”
Prior undertook wicketkeeping drills yesterday and batted for an hour against a variety of bowlers in the nets.
The 31-year-old wore strapping tape over the left calf he injured during England’s warm-up match against Australia A in Hobart earlier this month, but looked generally sound in his movements.
Prior spent quite a bit of time facing the off-spin of Graeme Swann under the watchful eye of England batting coach Graham Gooch.
He also undertook a series of runs between the wickets during net practice to test the damaged calf a little more strenuously.
Bairstow is Yorkshire’s first-choice wicketkeeper, but has yet to don the gloves at the highest level.
The 24-year-old has also been working hard in the nets and has undertaken extensive keeping drills ever since Prior was affected by injury.
England must weigh the possibility of short-term gain against the prospect of long-term pain when it comes to deciding one way or the other.
If Prior pulls up on the first morning of the match, the decision could backfire, although Bairstow would be determined to show otherwise.