Jose Mourinho has confirmed that Nemanja Matic will miss the start of the Premier League season after undergoing abdominal surgery in the United States.
Matic played the full 90 minutes in all three of Serbia's matches at the World Cup, but he has not featured at all for Manchester United in pre-season.
Mourinho confirmed that the 29-year-old had flown to Philadelphia to see a specialist and was immediately booked in for surgery.
"Matic came from the World Cup with an injury and the time he had to rest on holiday was not enough to resolve the problem," Mourinho said, as quoted by BBC Sport.
"He went to Philadelphia for a top specialist and he didn't leave the clinic. He immediately had surgery."
Matic has now returned to Manchester to continue his rehabilitation, but he will not recover in time to face Leicester in the Premier League curtain-raiser on 10 August.
This news comes as a blow to Mourinho, who values Matic among his most consistent performers in a squad which contains many players that he does not trust.
In Matic's absence, United were thrashed by Liverpool in Michigan on Saturday, losing 4-1 in a match that Mourinho said he would not have paid to watch if he were a supporter.
United's weakened team - including five players who didn't play a minute of Premier League football last season - is an indication of Mourinho's frustrations with the pre-season schedule. Many of his players are still on holiday after the World Cup.
Mourinho still wants to strengthen his squad ahead of the transfer window closing on August 9.