Luke Shaw's competitive debut for Manchester United has been delayed after he suffered a hamstring injury, which has ruled the England international out for four weeks.
The left-back missed United's final pre-season friendly against Valencia with the problem that will force him to miss the club's first four games of the campaign, including the Premier League opener against Swansea City, and England's opening Euro 2016 qualifier against Switzerland.
The 19-year-old is now likely to have to wait until September's visit of newly promoted Queens Park Rangers to make his bow for United, whom he joined from Southampton for £30m this summer to make him the most expensive teenager in world football.
"Luke Shaw has suffered a hamstring injury and will miss the opening game of the season against Swansea City on Saturday," a club statement said.
"Shaw sat out the friendly victory against Valencia at Old Trafford due to the problem and faces a wait before making his competitive debut for the club."
The blow potentially leaves new United manager Louis van Gaal without seven players for the opening game of his tenure against Swansea at Old Trafford.
Jonny Evans and Antonio Valencia have both suffered recent injuries and join Shaw on the treatment table ahead of the start of the campaign.
Robin van Persie and Michael Carrick will also miss the start of the season, with the Netherlands forward yet to return to full training following the World Cup, while the latter suffered an ankle injury in the first week of pre-season.
Belgium pair Marouane Fellaini and Adnan Januzaj have featured for just 14 minutes in pre-season and are not expected to be risked this weekend having only recently returned to training.
United ended their preparation for the new season with a 2-1 win over Valencia but Van Gaal was preoccupied by the club's growing injury list.
"Fellaini and Januzaj have only been with us training for one week," he said. "They can't play any more minutes than they did [on Tuesday] tonight.
"We have a lot of injuries now. Don't forget, Jonny Evans was injured, Luke Shaw was injured, Antonio Valencia was injured. These are three defenders. We have to wait to see if they can play on Saturday. The main thing is that we have won, despite playing our worst game."