Krol is not being asked to be the last man in defense or sweep behind, though. His remit is to be a proactive blocker of passing channels - which is one of the ways Zico will try to bring Romário into the game. My bad for either messing up the terminology, or not making it clearer in the formation graphic, but with 2 arrows on Sharemytactics, you can only do so much in terms of expanding on the details. I guess the type of situations he can help with is something like this (among other similar-ish configurations):
If you study Ajax's defense, Krol would frequently pop in to cover for Blankenburg as a part of their totaalvoetbal scheme in defense where they often moved around and changed positions, or station himself just ahead of the latter while the wide midfielder covered the outside channel. Similar with Haan when they played for the Netherlands with Krol going inwards (not behind the defense) while Van Hanegem and Rensenbrink spread out. While Krol isn't playing in a totaalvoetbal scheme here, the principles of his defensive awareness remain the same, and since he has a bit of breathing room in the absence of an extremely threatening winger or a productive wingback in the mold of Cafu, he will definitely have the time to device strategies for passing options that can be intercepted by him.