Trippier and Llorente were largely excellent last season in the title win. It's obvious Trippier wants to go back to UK now and is running down his deal so he'll be sold in Jan.
Lemar only ever really been a bit part player for them and he's never really got Felix into his team structure consistantly tbh.
I think Aleti's biggest problem has been decline of Suarez as he popped up so often with late winners for most of last season. Greizzy returning hasn't worked out at all either.
I'd still fancy them v Man. United though as things can change in two months and they've consistently shown v english teams in knock out rounds their style is very hard to defeat over two legs. Ronaldo could of course be decisive like he has been in previous match ups.
Personally if I were Simeone, Lemar and Felix would be starters. Both are excellent on the ball, maybe not as defensively good but with the talent like that they should really be aiming dominate and outscore their opponents. Both have largely been good when played so it surprises me they're bit regulars.
Another I'd start is Angel Correa. He hasn't been given as much game time since Griezmann came in, but he was also huge for them last season with some very crucial goals and assists.
With Trippier back from injury I'd honestly consider a switch to 4-3-3 for them. A team of the following would blow past most teams in the league, even Real in a heads up:
Felix - Griezmann/Suarez - Correa
Lemar - Koke - Llorente
Defense - Trippier
Oblak