Speaking at an Old Trafford press conference to unveil the pair of new signings, the United manager admitted: "We could possibly bring one or two more in. When there's a major international tournament on there's a delay in the transfer market. But now the European Championships are over we're trying to bring someone in.
"We've always done well in terms of getting players at the end of season, instead of waiting all summer. In Kagawa's case, there was a fair bit of negotiating and that kept going for weeks. As for Powell, we knew Dario Gradi [Crewe Alexandra director of football] would help us do the deal quickly."
Sir Alex discussed Powell's best position with Gradi, having seen him operate mainly as a deep-lying forward for Crewe. "I asked Dario if Nick could be a central midfielder. Dario thinks that's his position and Nick does too so we're all in accord. We hope he'll be a central midfield player and that's where we'll develop him."
As for Kagawa's role, the boss said: "He'll play further forward [than Powell]. We shouldn't be looking at one player changing the way we play but he could make a difference. He can give us that extra in the final third of the field. If his goalscoring record continues he could be a very good player for us."
Kagawa was Borussia Dortmund's second highest scorer last season, and after acclimatising himself to European football with two successful campaigns in Germany, the Japanese international is poised to pick up the English game very quickly.
"Shinji's coming to South Africa with us and then to China so I think you'll be seeing him