England's talisman Ben Stokes has bowled and fielded with a jarred knee at the Gabba, while Australia have their own injury scare after David Warner failed to field because of bruised ribs.
Warner was notably absent at the start of England's second innings in Brisbane, still feeling the effects of a blow he suffered while batting.
Stokes, boasting a unique ability to win games with bat or ball, loomed as the man most likely to hurt Australia in this Ashes.
That may still transpire with the combative allrounder often producing his best when England are under the pump.
But the allrounder's setback, coming as the hosts put Jack Leach to the sword while seizing control of the series opener, proved untimely on several fronts.
Stokes, playing his first competitive match since July because of a finger injury and mental-health break, delivered 12 overs in total during Australia's first innings.
The vice-captain, cleared to bowl after being assessed on Friday morning, managed three overs on day three.
Stokes' lack of potency meant Joe Root was forced to turn to his frontline quicks more than would otherwise be the case, with paceman Ollie Robinson also pulling up sore on day two.
The second Test begins at Adelaide Oval on Thursday, giving Stokes limited time to recover from the knee problem.
This five-Test series has been squeezed into six weeks, meaning similar short turnarounds in coming weeks will test the resolve and fitness of several players on both sides.
Stokes appeared to hurt his knee in an early fielding mishap and was clearly restricted for the rest of Australia's first innings, while Robinson clutched at his leg and trudged off the ground after delivering his 18th over.
Robinson notably didn't take the second new ball late on Thursday.
But the right-armer rolled his arm over on Friday morning, allaying fears it was anything serious.
"My body is doing OK," Robinson said after play on Thursday.
"I came off for some strapping and maintenance."
