Celtic were eliminated from the race for the Champions League after Austrian opponents LASK overturned a four-goal aggregate deficit to win the tie 5-4. The result means the Scottish side will miss out on the continent's premier club competition for the second season running.
Manager O'Neill acknowledged his role in the collapse, saying he accepted responsibility for the team's performance. He addressed the media after the match and reflected on what went wrong over the two legs, signalling a readiness to answer for the exit.
The turnaround by LASK capped a dramatic tie that will be remembered for the visitors' resilience as much as for Celtic's failure to protect a substantial advantage. The result represents a major disappointment for the club, which had looked on course to progress before the late reversal.
Attention now turns to how Celtic respond on and off the pitch. The elimination complicates the club's European ambitions and deprives them of the financial and sporting benefits that come with Champions League qualification; the manager and squad will face scrutiny in the build-up to the domestic season and any remaining continental fixtures.
LASK's progression will be celebrated in Austria as a notable achievement, while Celtic must regroup quickly. The aftermath is likely to prompt questions about personnel and strategy as the club seeks to stabilise after a costly European setback.