Joey Carbery could miss next year's Six Nations because of the ankle injury that wrecked his Rugby World Cup.
The Munster fly-half, who underwent surgery prior to the World Cup after damaging his ankle against Italy in August, was restricted to three substitute appearances in Japan as Ireland once again crashed out at the quarter-final stage.
"Joey is going to be out for some time," said Munster head coach Johann van Graan. "We've got to make sure he gets his strength back and we get that ankle fully functional.
"From Joey's point of view, obviously, he wants to play but his body is not right. Because of the type of injury he is definitely not going to be back in the next few weeks."
Munster will be without the 24-year-old for the opening four rounds of the Champions Cup, including back-to-back games against defending champions Saracens in December.
Van Graan confirmed Carbery does not require further surgery on his ankle but says they must be patient with his rehabilitation.
"He is very important for the national team, I believe, for the future of Irish rugby," Van Graan told the Irish Times. "I am not the coach but I imagine Andy Farrell will look at him.
"For Munster he is a game winner, that's why we got him and that's why we want him on the pitch but we don't want him to play for a week and get injured again.
"Joey is one of our star players. The 25 out of 25 that he kicked last year showed that when he was on the field he made a big difference to our play. He did some very special things.
"At the back end of last season we didn't have him for the [Saracens] semi-final and he literally came back against Leinster, played for 60 minutes and went into the national team, went to the World Cup that I am not going to comment on, but he came back to us now."