"Shinji's coming to South Africa with us and then to China so I think you'll be seeing him pretty soon," said Sir Alex, looking ahead to Monday's start of the DHL pre-season tour.
"Once he's adapted and gets to know some football phrases our players will use, he'll be used to that. He can start the first league game quite easily. I've got no problem with that."
Powell may have to bide his time for a competitive debut but he too will be on the pre-season tour.
"I think in Nick's case, he's got a bit of physical development to do, just as we would expect of an 18-year-old. But he'll be in the first-team squad and train with us every day."
The England youth international could still make an early impact, however, in keeping with the proud traditions of Manchester United.
"Football throws up opportunities for young players and we play young players all the time," Sir Alex said.
Look out for more stories - and quotes from the new signings - on ManUtd.com this afternoon (Thursday).