Both ties will feel little more daunting without Kane or Son, and any shot at a return to the title race feels highly unlikely after this defeat, despite the positive noises about how well they played only to be denied by the brilliance of De Gea. Here are three takeaways.
It might be different if Spurs were active in the transfer market but they have an expensive new stadium to fund and have not signed a senior player since Lucas Moura, almost a year ago. It is a fantastic finish that just shows practice makes flawless, because he has been practicing lately in that position.
The England worldwide is regarded as one of the most consistent strikers in the world and struggling Los Blancos want him to revamp their squad.
Just ideal all around.
Tottenham have also rejected bids from the Spanish giants for Kane's teammate Christian Eriksen as the Danish global is arguably playing the best football in his career this season.
"And how I shouted at the goal of Manchester United was unbelievable". But consider that United's goalkeeper had 11 saves on the night, many of which were from close.
The Reds have won all five of their games under the Norwegian's charge so far, although this weekends game against Spurs is quite comfortably the most hard that they will have faced. After six or seven saves, you just felt like he would save anything that came at him.
One fan tweeted: "Kane injured and Son gone to the Asian games".
It was a decision to bring management temporarily back in house with their former striker, tap into United's former values and revive a squad that seemed to be leading a life of abject misery under Mourinho. Their campaign is back on track. "The team spirit is fantastic and, secondly, we've shown we can defend today".
United have a proud history of producing their own talent, having included at least one youth-team graduate in every first-team matchday squad since October 1937. Plus, they also conquered a solid 2-0 win over Reading in the FA Cup. De Gea was a huge reason why this team took the loss at home, and now it's time to rebound.
Manchester City finish third, Tottenham are fourth and Liverpool and Chelsea have to settle for fifth and sixth respectively.
Next: United hosts Brighton on Saturday at 10 a.m., while Spurs go to Fulham on Sunday.