Sir Alex Ferguson has admitted that Darren Fletcher's career is in the balance due to a chronic bowel problem, although the Manchester United manager said that should the midfielder be forced to retire, he will be offered a position with the Old Trafford club. Fletcher, who is 27, last featured for United in a Champions League match against Benfica in late November and has not trained since.

"He has obviously got great challenges ahead," Ferguson said. "We are happy to be patient but he won't be starting the season. It is unfortunate because he is such a magnificent professional and such a nice lad. If it doesn't work for him, he knows he has a position at the club anyway."

Fletcher has become one of Ferguson's more important players. He made his debut for the club in 2003 and has started in 164 Premier League matches.

Ferguson, who refused to take any questions on the Glazers' flotation of United on the New York stock exchange, was speaking at a media conference to unveil his summer transfers, Shinji Kagawa, the £12m signing from Borussia Dortmund, and Nick Powell who cost £4m from Crewe.

Regarding any further recruitment, United's manager said: "It's possible we could bring in one or maybe two more. Where we've always done well in terms of getting players at the end of the season. We always feel that it's the right time. We don't have to wait the whole summer. In a European Championship or World Cup year there is a delay in the transfer industry. That is over now and we are still trying to get one more in."

Of Kagawa, who scored 19 goals in all competitions for Dortmund last season, Ferguson said: "He plays in behind the striker, he's very quick, and he's got good vision. His goalscoring record over the last two years has been very good from that position.

"It was good that he was with a successful team to allow him to adapt to European football. He's a maturing player and in the next few years we'll see that at United. It's a good time for him to come to us."

Ferguson often played a 4-4-1-1 in the Premier League or a 4-5-1 in Europe. So would Kagawa's presence mean United will adjust their style? "We shouldn't be looking at one player changing the way we play but he could make a difference," the Scot said. "He can give us that bit extra in the final third of the field. If his goalscoring record continues he could be a very good player for us. We expect that [he will be exciting]. He'll go on the [pre-season] tour and that gives him an opportunity to get to know the players and acclimatise to the way we are. Also there's the issue of the language. I'm sure over the next few months he'll improve his English."

Ferguson added that United had been watching Kagawa since last autumn. "We have a scout in Germany and he recommended him at the end of October," the manager said. "He had a good season the year before [when joining from Japan's Cerezo Osaka]. But sometimes when a player goes into a new league the first season is new for him, the second season is a better test."

Kagawa is clear that he can handle playing for United. "I definitely feel the attention of the media globally now I'm a member of a great club like Manchester United. But I think I can take the pressure. I'm pretty confident I can adapt to the Premier League style," the 23-year-old said.

Ferguson added that he views Powell, 18, as a central operator. "Although Crewe played him as a forward or behind the striker we see him as a central midfield player. Hopefully we'll see that progress."

Powell said: "It's a whole different world. At Crewe it's one camera and one person, Manchester United is the whole world. So from Crewe to United is the biggest step.

"The players have been fantastic. Everyone speculates about the big-time and stuff like that but they've all been very nice and welcoming. I've still got a lot to develop and coming to Manchester United will help that, but I'm not near my best."