The Mexican came on for Ander Herrera after the hour-mark and proceeded to miss a penalty and sky a tap-in from just yards out.
Despite winning 7-1 on aggregate to book their place in the Champions League group stage, Van Gaal look seething at Hernandez's performance.
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Louis van Gaal stares down Ryan Giggs in Bruges
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After seeing the former Real Madrid loanee slip over and fluff his penalty, Van Gaal shot assistant Ryan Giggs a killer death stare.
And eagled-eyed viewers were quick to discuss the comical exchange on Twitter...