Nani was impressed by Januzaj's contribution on Wearside after the teenager's double strike clinched an important success.
"It was a good day for him," said the skilful wide man. "We know he has good skills and is a good player. He has chances to push on and I hope he can help us more in the team."
The World Cup qualifiers now take Nani's focus, with his country hoping to qualify from Group F. Portugal sit a point behind leaders Russia ahead of a home double-header against Israel and Luxembourg.
"We need to win the next games and see if Russia drop points," he added. "But we will focus on winning our own games.
"We are virtually at least in the play-offs but we will see what is going to happen this week.
"It's totally different to play for Manchester United and play for the national team. I think the spirit will be very good after we go away for these two games with the national team as we'll then be back to full time with United and hopefully we can try to do our best."