"He's [Januzaj] a great prospect," Rooney said.
"He takes the ball, he runs at players and he's got great ability. It's great the manager has thrown him into the side, especially with what has happened in the last few games.
"There was big pressure on us but the manager has trusted him and he has repaid that. He's very confident - that's great to see.
"A lot of the young players who come through are a little bit timid and shy but he looks comfortable and he's confident in his own ability, which you need to be. It was a brave move to play him in the circumstances and we’re delighted it's paid off.
"There is a lot of pressure but he seems to thrive on it. We know the ability he has got but you never know how they are going to react when they are thrown into games.
"We need to help the younger players and, if we do that, they'll be moments where they come in and win us the game, as has happened here. The experienced lads need to help them emerge into a team."
Januzaj, who is of Kosovan descent, was born in Belgium, and is eligible to play for a number of other countries including Albania, Turkey and England.