Roy Keane is to have an operation to his knee that may keep him off the pitch for three months.
His right knee seized up during the Republic of Ireland's 2-0 win against Iran on Saturday.
That match was the first leg of the World Cup play-off and his injury means Keane won't be taking part in Thursday's return leg in Tehran.
The knee injury has already meant Keane's missed five games for his Manchester United side.
The 30-year-old now may miss up to 15 Premiership games, two Champions League ties and three rounds of the FA Cup.
Keane damaged the cruciate ligament in a knee four years ago which put him out for 10 months.