Joey Carbery is set to miss the remainder of Ireland's Six Nations campaign, while he is now also considered a major doubt for Munster's Champions Cup quarter-final against Edinburgh next month.
The Irish Independent understands that the hamstring injury Carbery suffered in training last week is much more serious than first feared, and he will not play in either of Ireland's remaining games against France or Wales.
The news will come as a big blow to Joe Schmidt, who was eager to give his back-up out-half more game-time ahead of the World Cup.
Carbery got eight minutes off the bench against England before he was sprung into action after just 23 minutes the following week in Murrayfield.
As a result, the Ireland coaching staff will take every precaution and will not release Jack Carty to play for Connacht this weekend.
Carty, who made his debut in last weekend's win over Italy in Rome, will instead be involved in Ireland training this week with Leinster's Ross Byrne expected to earn a recall as extra cover.
Schmidt had been hoping that Carbery would be fit in time for the France clash next weekend, but the 23-year-old is now believed to be set for a prolonged spell on the sidelines.
The setback means that Munster are also sweating over Carbery's injury ahead of their European clash on March 30 and beyond.
Johann van Graan admitted on Monday that Carbery would be "out for a few weeks" and the Reds' head coach will hope that the hamstring problem will not keep his star man out for as long as is now feared.