Jose Mourinho has confirmed that Nemanja Matic will miss the start of the season, due to an injury problem sustained at the World Cup.
Matic joined the pre-season tour on 22 July and trained with the squad for the first time two days later, but played no part in Wednesday's 1-1 draw with AC Milan in Carson, California.
Following Saturday night's 4-1 defeat against Liverpool in Ann Arbor, the manager confirmed that Matic had left the tour to undergo surgery.
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“Matic arrived from the World Cup, holiday, direct to surgery because something happened in the World Cup,”said Mourinho.
“He has had surgery. He is out for the start of the season. He came from the World Cup with the injury and the time he had to rest on holiday was not enough to resolve the problem.I don't know how long he will be out for,
“ admitted Jose.
There was further concern for United when Chris Smalling was removed from the starting line-up to face Liverpool, just minutes before kick-off as a precautionary measure.
The defender came out of the warm-up but was replaced in the team by Eric Bailly, who partnered Axel Tuanzebe and Tim Fosu-Mensah in the back three.
United's tour of the United States comes to a close on Tuesday, when the Reds face European champions Real Madrid in Miami.
A match against German champions Bayern Munich brings pre-season to a close on 5 August, before the Premier League campaign gets under way on Friday 10 August, as Leicester City visit Old Trafford.