The win against Ajax in Stockholm might have saved Jose Mourinho after his first season in charge at Old Trafford, as United only managed a sixth-place finish in the Premier League.
"I think the Europa League final was internationally our most important match in the last several years because we won the competition and that victory brought us to Manchester United's natural habitat, which is the Champions League," Mourinho said at a press-conference ahead of the return leg.
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The fixture is deadlocked at 0-0 after the first leg in Spain with the Red Devils' crosstown rivals Manchester City, Real Madrid and Liverpool all having already clinched their spots in the last eight.