Sir Alex Ferguson has confirmed he expects £18.6million signing Michael Carrick to be out of action for at least three weeks after sustaining ankle ligament damage in Saturday night's win over Ajax.
The England midfielder suffered the problem just 14 minutes into the game after being on the wrong end of a tackle by hosts' skipper Kenneth Perez.
Although Carrick tried to continue, it was obvious the pain was too much and he eventually left the stadium on crutches.
On only his second appearance since completing his move north from Tottenham, it was a devastating blow for Carrick, which will rule him out of the season Premiership opener against Fulham, as well as possibly games against Charlton and Watford.
'It is ligament damage to the ankle,' said United boss Sir Alex Ferguson.
'It is difficult to say what will happen with these things because we don't know what his general recovery time is but it will be three weeks at least.
'It is a blow for the young lad because he has only just joined us and he wanted to do well. It knocks him back a bit but it's something we have to handle as we have done many times in the past.'
Carrick's injury capped a dismal couple of days for United in the Dutch capital.
They were already without injured trio Gary Neville, Nemanja Vidic and Gabriel Heinze, while Cristiano Ronaldo, Louis Saha and Mikael Silvestre were not deemed fit enough to travel.
United then lost Rio Ferdinand to an ankle injury sustained in the warm-up prior to yesterday's win over Porto and John O'Shea picked up a dead leg in the same game.
Wayne Rooney and Paul Scholes are also facing the possibility of starting the season with three-match bans following their dismissals against the Portuguese champions.
'Your hope for the start of every season is a clean bill of health,' said Ferguson.
'The last two years have been horrendous for us in terms of injuries. I was hoping we would get a free run this year but it hasn't happened.
'But we have a big squad and we have to get on with it. We have great experience and hopefully that will give us a good chance.'
Ferguson confirmed his intention to play Rooney, Heinze, Saha and Silvestre against Oxford on Tuesday and also restated his belief there will be at least one new addition to his squad over the next fortnight.
'I am confident of bringing in one more player before the season starts,' he said.