As others have said, he is a defensive monster but if you look at what we have at our disposal already - in terms of midfielders, bringing in a ball-winning midfielder wouldn't really compliment the players we currently have.
What we need to think about, is a player who can compliment Fred or McTominay, and to me, that wouldn't be Ndidi, in my opinion. They just wouldn't be much balance to our midfield.
We even see for Leciester that the balance is made by having a good ball-playing midfielder in Tielemans next to Ndidi, which also worked pretty well when playing Medy in there, too.
Some would argue that Pogba is that player for us, and I agree but I'm not convinced Pogba is staying beyond this season.
Therefore, emphasis should be even more on trying to acquire a ball-playing midfielder, who is defensively astute, whilst having the likes of Fred/McTominay to do the 'dirty work', so to speak.
If we want a solid base, I think, for now, McTominay and Fred are enough. If we want to play on the front foot more often, especially against the top six, then it's crucial we get a ball-playing midfielder.
If Pogba does stay beyond this season, then a young player who shares similar attributes to the aforementioned player would be a clever signing. This is possibly what Ole was going to do with Caicedo.