AZ have a promising team and are doing really well in the Eredivisie this year, being 2nd in the league with only 3 points behind Ajax and way ahead of PSV.
Their team is very young with a lot of potential, especially with 'good old' Ron Vlaar being injured for this match, alongside their other CB Hatzidiakos, who recently made his debut for the Greek national team.
Their most promising players are Right Winger Calvin Stengs and striker Myron Boadu. Both still have to turn 20 but recently made their debut for the Duthc National team. (Ahead of players like Kluivert, Weghorst, El Ghazi) Two other players Teun Koopmeiners (21, captain, CDM) and Owen Wijndal (20, left back) are already being linked to invitations for the National team.
Besides that their teams holds of two Norwegian national team starters (Svensson, right back) and Midstjo (CM), and El Idrissi (left winger who got recently his first call up for Morocco), plus a goalkeeper Bizot who currently is in the running to beat the all time record for most clean sheets for a Dutch team in a year ever.. And then there is Jordy Clasie.. Another player like Dani de Wit (CAM) is someone from the Ajax academy who is a victim of Ajax' development and would have broke through there lets say 4 years ago.
Not saying United arent favourites ofcourse, not trying to make them better than they are cause all have a lot to prove still obviously.. They arent however to be underestimated. They are also already qualified so have nothing to lose.. If United play too many youngsters or dont take it seriously at all, the might have a very tough evening..