Ulster Academy back-rower Azur Allison has been ruled out of the Ireland Under-20s' World Championship game with Australia on Saturday (2.30pm UK-time kick-off) with a head injury.
Allison was replaced during Tuesday evening's impressive win over England that, even in a daunting pool, has given the side hope of making the last four in Argentina either as the winner of Pool B or as the best runner-up.
The Ballymena man has had a luckless run of injury having also missed out on the Six Nations Grand Slam won by Noel McNamara's side earlier this year, but could yet return in the concluding pool clash against Italy.
In his absence, a few of his Ulster team-mates shone. Centre Stewart Moore marked his debut at this level with a first-half try, while flanker David McCann bagged a brace of tries after the turn to help Ireland secure the bonus-point 42-26 triumph.
It was Ronan Watters who took Allison's place in the back-row on Tuesday and, after an impressive display, could well get the nod again, while Ireland will have to weigh up more changes after such a bruising opener.
Australia also got off to the perfect start on Tuesday with a comfortable 36-12 win over Italy.
Australia, under-age champions of Oceania, led 36-0 and had their own bonus-point wrapped up by just after the hour mark.
Reflecting on the enthralling 42-26 win over England, McNamara said: "It was obviously a strange game with the three yellow cards that England experienced.
"Tactically for them, they were trying to slow the game down and almost while away those periods, whilst we were obviously trying to do the opposite.
"So it certainly presented us with challenges and I think our tactical approach could have been a little bit better in how we managed those periods when England were down a player.
"I suppose we invited some pressure on ourselves and conceded a couple of tries that we really wouldn't be happy with.
"I think discipline is so important. It's obviously one of the areas that we have had a big focus on throughout the course of the year.
"I think that was really evident (against England)."