Manchester United captain Roy Keane is likely to be out for two months after breaking a metatarsal in his left foot.
Keane suffered the injury to his third metatarsal in United's 0-0 draw with Liverpool at Anfield on Sunday.
The 34-year-old was only just back after missing the Champions League game at Villarreal with a hamstring injury.
It is also a blow to the Republic of Ireland's World Cup hopes as Keane looks certain to miss their final qualifier against Switzerland.
He is already suspended for the next World Cup game against Cyprus on 8 October and, if the initial diagnosis is correct, he will miss the match at home to the Swiss four days later.
United officials confirmed Keane suffered the injury - the same one which has sidelined David Beckham, Gary Neville and Steven Gerrard in recent years - in a late challenge with Luis Garcia.
Keane was a surprise inclusion in the United midfield as he was expected to be out until the end of the month with a hamstring injury sustained against Manchester City.
But the injury responded well to treatment, enabling him to play in the game at Anfield.
However, he now looks like missing a vital part of the season, including their next three Champions League games and the visit of Chelsea on 6 November.