Sir Alex Ferguson claimed that Manchester United had completed their transfer market activity this summer when he unveiled Michael Owen as the club's new No 7 today.

It is thought the club are interested in signing Douglas Costa, the highly rated Brazil Under-20 midfield player, from Grêmio, but the United manager said that his current squad is good enough to challenge for an unprecedented fourth consecutive league title this season.

"It is the end of our business, so all these stories about who were are supposed to be getting - forget it," he said.

The Brazilian club are holding out for about £20 million — close to the release clause stated in the player’s contract — but United are reluctant to pay that much.

United initially wanted to take Douglas, 18, on a three-week trial, but while that request was rejected by Grêmio, negotiations over a permanent deal have been continuing.

Douglas would be United’s fourth signing of the summer after Owen, Antonio Valencia and Gabriel Obertan, with senior sources at the club insisting that they have no interest in buying Samuel Eto’o, the Barcelona striker.

United lost out to Real Madrid for the signature of Karim Benzema, the Lyons striker, when the Premier League club refused to be drawn into a bidding war for the player despite recouping £80 million from the sale of Cristiano Ronaldo.

"There are some amazing numbers being talked about, not all of them realistic," Ferguson said. "It is very difficult to get value now. I feel we have a good squad, which meant there was no need for knee-jerk reactions. We asked about Benzema and we had a value for him. Lyons have done well because they got €42m (about £36m) but I think we took a sensible view."

Owen inherits Cristiano Ronaldo's shirt number and his place in an attacking line-up containing Wayne Rooney, Dimitar Berbatov, Daniel Welbeck and Federico Macheda.

“I’m hungry to do well here,” Owen said. “If this challenge doesn’t put a spring in your step and a smile on your face then nothing will. I still believe I can do well at a top team like Manchester United.”

Owen also refuted claims that he is injury-prone after two disappointing seasons at Newcastle. "It does irritate me that so many people have doubts," he said. "If there is one thing I am angered by, the injury thing would be it.

"There is no doubt I have had injuries in my career. But there is a long list of players that have had a broken metatarsal. I was foolish trying to rush back for the World Cup and my leg had just come out of plaster. But I played 33 and 32 games in the last two years in a team that was not in Europe and did not go on a decent cup run. Still I was continually labelled injury-prone, which gets up my nose.

"I am 29 and have played over 500 games for club and country. That says it all."