The 18-year-old was not in the 'A' list as he became eligible to join the 'B' list from 7 October. And now, having sat out the first two Group A matches, Januzaj is ready and available for selection.
Speaking during his pre-match press conference on Tuesday, Moyes also revealed that Danny Welbeck and Tom Cleverley both "have a chance" of facing the Spaniards at Old Trafford, whilst also offering an update on the fitness of Rio Ferdinand and club captain Nemanja Vidic.
"There are one or two knocks and niggles, which most teams have. Vida and Rio are making good progress. Danny Welbeck has a little bit of an injury from the Southampton game so we'll have to see how he is. Tom Cleverley isn't as bad as we thought. They both have a chance."
"Januzaj is available," Moyes added. "He's an exciting young player and he's making good progress all the time. He's someone who, I'm sure, will play a big part in the future of Manchester United. He's an exceptional talent."