The young winger has agreed a season-long loan switch to the Black Cats to link up with David Moyes, the man who gave him his big break at Old Trafford.
The move should offer Januzaj a route to consistent first-team football at a Premier League level, and Mourinho explained that this was the reason he sent the youngster to an English club – rather than to another foreign side.
“He fits my plans,” the Portuguese boss said:
“That’s why he is on loan at a Premier League club. If he doesn’t fit I don’t care about him, don’t care where he’s going, which club, which competition, which manager.
“Maybe I send him to Borussia Dortmund. Yes, we care about him, we think he is a talented player but to be in the same squad as Martial, Mkhitaryan, Young, Depay would mean not many matches.”
Manchester United fans, after three years veering between disappointment and disenchantment under Moyes and Louis van Gaal, are expecting a change of pace under Mourinho’s management.
After making some significant statements in the transfer market, he is now looking to do so on the pitch – starting on Sunday.
Asked what the club’s followers could expect from his team, he said: “Professionalism, that’s for sure.
“We’re not here to have fun, not here to enjoy the sunny weather. We’re here to work, here to give everything for the club.
“That’s what we promise. The only thing that every Manchester United fan around the world can be sure of is that inside the training ground everybody works.”