The midfielder only pledged his allegiance to Belgium - the country of his birth - last month.
"Adnan is the kind of player who could light up a World Cup, whether that is starting games or off the bench," said the United interim player-manager, who started Januzaj in the 3-1 win over Hull on Tuesday.
"I was excited when he got the ball the other night - when I was on the pitch and on the bench.
"He floats with the ball effortlessly. He is just one of those players you love watching."
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