The new purchase Michael Carrick, who participated in a friendly tournament in Amsterdam, suffered a left foot injury during a match against Ajax on Saturday and may miss the start of the English championship.
The midfielder played only fourteen minutes in his second match with the Red Devils and left the field after being roughly tackled from behind by a player from the Dutch club.
"It looks like he'll be out for a few weeks, his foot is very swollen," said the team's manager Sir Alex Ferguson.
A penalty kick by Ryan Giggs secured a 1-0 victory for the team, making Manchester United the winners of the Amsterdam tournament after defeating Porto 3-1 on Friday.
Carrick made his debut in the match against Porto, where the Red Devils finished with less than a full squad. Wayne Rooney was sent off the field for the fourth time in his career, while Paul Scholes, known for his rough play, could also face penalties from the English Football Association.
Manchester United will play their first Premier League match against Fulham on August 20, and Ferguson is concerned about injuries to Gary Neville, Gabriel Heinze, and Nemanja Vidic.
Rio Ferdinand and John O'Shea suffered injuries in the match against Porto, but both players should recover before the start of the season.
"Our hope before the start of every season is to have all players healthy," the Scot added. "The past two seasons have been terrible for us due to injuries. I hoped the whole team would be healthy and start the season at full strength, but unfortunately that did not happen. However, we have a great team and we need to continue working with them. We have experience and I hope it will help us."
It is worth noting that the 25-year-old defender, recently added to the Manchester United squad, was acquired from Tottenham for £18.6 million.