Spain is weak on the center. Going small-ball with Reyes won't work as no matter how much I value the things he does on court he isn't the kind of guy I expect stoping Raduljica and Kuzmić repeatedly, Hernangomez is a good talent, yet too young to make a noticable impact.
Looking at the rooster I'm seriously wondering if Scariolo would decide to use Mirotić at C to stretch the floor to hurt Raduljica and try playing with some mobile lineups when Pau won't be on the floor, while trying to pressure on Serbian guards to eliminate their chances for a succesfull half court inside play along that.
Than again rebounding will play a major role, especialy if going small ball, as I don't doubt Spaniards will try making the best out of their speed, where I've got a feeling Serbia doesn't excell defending those. On previous occasions it sometimes seemed Spain was too dependent on their defense, as apart from some obvious and simple offensive solutions or going 1 on 1 they relied on fast breaks to a large degree.
If Serbia manages to slow down the pace and play a smart inside-out game, be consistent in offense and stop those fast breaks through smart fouls, offensive rebounding, little TO's or fast sprint in defense their chances would increse as I don't expect Spain to change their game enormously from previous tournaments. Spain on the other hand has a chance in stretching the floor and trying to out-defend the Serbs on the perimeter. I think we might get to a point when both teams would be attacking the centers. Serbia because after getting Pau into foul troubles would pretty much be sweet for them and Spain trying to abuse Raduljica's defense that's not on the same level as his offense and basing their offense from there on as Spain rarely uses some complicated combinations in offense.