Calling MU serious contender is just silly, yes they have the chance to make it to the final or even winning it (so are teams like Porto or Ajax) but that's a different story and it requires massive luck for them to make that achievement. Their squad is nothing special, they even played some youth players against PSG whose name so hard to spell lol
Serious contender is for team like Juve, Barca, Pool, and City. Teams with talents all over the pitch, though Juve and City might choke at some point