Rio Ferdinand will miss Manchester United's first three Premier League games, as well as England's European Championship qualifiers with Bulgaria and Switzerland in September, due to the knee problem that kept him out of the World Cup.

Ferdinand had hoped to start the season but will miss another six weeks after Sir Alex Ferguson, the United manager, confirmed the defender had sustained ligament damage. There is little prospect of Ferguson allowing his key centre-back to join up with England before he is fully fit, meaning he is likely to return for his club at Everton on 12 September.

United denied suggestions that Ferdinand faced a considerable spell on the sidelines earlier this summer, insisting he was in the running to face Newcastle in their opening Premier League game, but Ferguson is sure to tread cautiously with a player who has been hampered by injury for the last 18 months.

Ferdinand, who is now an avid user of Twitter, has insisted there is nothing sinister in the setback as he begins his rehabilitation. He Tweeted yesterday: "Six weeks and I'll be playing again. At the start of rehab we put dates on these injury comebacks but sometimes the goalposts move a bit."

Ferguson has also revealed that striker Michael Owen will miss the start of the season as he battles back from a hamstring problem sustained in the Carling Cup final in February.

Defender Gary Neville is training again at United's Carrington centre after a calf problem ruled him out of the pre-season trip to the United States – where United faced Kansas City Wizards last night – and he was set to be joined today by winger Antonio Valencia, who has also been struggling with a calf injury. Midfielder Owen Hargreaves will remain in the United States, where he is receiving treatment for his long-running tendinitis problem and fellow midfielder Anderson is on course to return from an Achilles injury in September.

Ferguson insists he had little choice but to be vague about the future of Nemanja Vidic last week, just hours before it was announced that the Serbian defender had agreed a new four-year contract. The United manager claimed he could give no guarantees about the centre-half's future, with two years to run on his previous deal and Real Madrid said to be interested. But following another summer of limited transfer activity, Ferguson is clearly overjoyed at securing Vidic, who joined from Spartak Moscow in 2006, until 2014.

"In the modern-day game it is not easy renewing players' contracts when they do well, particularly those from other countries," Ferguson said. "Over the last year or so there has been speculation about Nemanja time and time again, sometimes by the press, sometimes fuelled by other sources.

"But we never had a strong feeling he really wanted to leave. There is always concern; if they do well they want better contracts. At the end of the day we have managed to achieve the task of getting him to agree a four-year contract."

Ferguson added: "We are delighted. He is a fantastic centre-half, a great competitor with a marvellous attitude to winning games. It strengthens our hand."