There are almost no players left from the team that Mourinho coached at Manchester United, so it will be a different team and yes, it will be weaker than before. Fenerbahce is also not the strongest club and in the last round they could not beat Twente, so it is not worth saying that they are now definitely stronger than Manchester United, they also played a draw with Twente and with a more difficult opponent Porto. Ten Hag's position is very shaky, any defeat for him could be the last in Manchester United.
Therefore I said Mourinho will fight his former club not his former protégé. At least Mourinho's tactics are much more effective than Erik Ten Hag, that's what I can see from both teams when they meet later. Just to remind you that any defeat that Man United gets will not make Erik Ten Hag fired, he seems to have strong backing behind the scenes, so that the bad results throughout this season do not make his status waver in front of Man United top brass. Ineos and Sir Jim do not seem to take a firm stance against him.
The weird part is, Twente looks to me as a better club than Manchester United right now. Obviously when Manchester United plays with 100%, then we saw what they can do, it's been only a few months since they won against City to win the FA cup, so we know what they are capable of. But this is also the same team that has been terrible at premier league this season as well.
So if they do play with their 100%, of course they are going to beat Mourinho and his Fenerbahce, but if they play like they did so far then there is a possibility of them getting destroyed as well. Twente, playing normally, is a better team than Manchester United played all season long this year, whereas United playing at 100% is better than any team in Europa. Their inconsistency is consistent, and I am not sure if we are going to see them get a win here. Fenerbahce has a level of playing, they are not terrible, not great neither, so this whole game depends on how United will play this one.