Tottenham perhaps has a lot of work to do in today's encounter as a result of their inability to score a single goal in the first leg encounter, they have to take advantage of fact that they are playing at home and most importantly, they have to try as much as possible to score an early goal that will cancel out the deficit they already have.
The first leg result was just a goal difference and it shouldn’t be too hard for Tottenham to equalize if they play well, the only problem they have is that Tottenham are not very consistent with their performance and if they should play the way they played in the first leg then they are likely to lose this game also.
Playing at home gives them the advantage but can they grab on to the opportunity? They need to make their home fans proud and progress to the next round by all means, they need to win on aggregate no matter what. I believe it is possible that they can turn things around.
For Manchester united, it already clear that they already hold the advantage at the moment but that still doesn't mean they have to relent because in these sort of encounter especially against Spanish sides, they suddenly might concede goals that they didn't expect thereby truncating their chances of progressing to the next round.
Manchester United also have the advantage playing at home but it is not a guarantee at all, they need to be at their best if they want to win, they are not so good at their home ground but since Real Soceidad are also not performing too well they can win and progress to the next round.