We may not see a great deal of him for Costa Rica either. Miller hasn't played for his country since an off-the-bench cameo against South Korea in Seoul last October. He is in the squad for this friendly against Spain because he is part of head coach Paolo Wanchope's preferred squad for the Gold Cup. But being in the squad is not the same as being a starter. This will be a chance for him to stake a claim to the starting lineup for the summer tournament.
Not the last chance: Los Ticos also have a friendly against Mexico scheduled for June 27. But Miller needs competitive minutes more than many in Wanchope's current squad. It will be interesting to see whether the coach takes this chance to give a (most likely) rusty Roy the chance to stretch his legs, or prefers to use him sparingly.
Costa Rica is up against a Spain squad readying itself for a trip to Belarus for Euro 2016 qualifying. The Spanish can be expected to hold a little back, since they will be playing a competitive game just three days after this one - that may tempt Wanchope into letting a few players who might not be at the peak of form and fitness have a run. This would be to RBNY's benefit, as Miller will be back with his club quicker than Kemar Lawrence (who is involved in Copa America until June 20, at least), and therefore should be in line for a start or two at left back when he is returned to Harrison.
Most of the Red Bulls could use a break, but not Miller: he's had a rough time with injuries and subsequently losing his place in the starting lineup to Lawrence (before being required to deputize as a center back due to RBNY's persistent injury, suspension and call-up issues). He needs minutes on the field - and this game is a good chance to get them.