The Portuguese 21-year-old arrived in the UK on Thursday as a £6million deal was being formulated to capture him from Benfica.
The move will not been completed in time for him to acquire international clearance to be involved in Saturday's Barclays Premier League trip to Reading. Moyes added: "Manuel was with us on loan last season, so he knows all about us and we hope he will be able to hit the ground running when he arrives.
"He knows about us and what we do, he will give us a different option. We are playing with Lee Carsley and Phil Neville just now in the centre of midfield and he will give us more competition there.
"But he is a different type of player, with a bit more craft. At 21 he was a big player in the European Under-21 championships for Portugal and we are delighted to have him."