With the game delicately poised heading into the half-time break, Gregoritsch was awarded a free-kick on the edge of the Hamburg box for an alleged infringement by Vieira.
But then, something rather unexpected happened. Instead of taking the set-piece in what was a very dangerous position, the former Hamburg striker turned to referee Deniz Aytekin and informed him that it wasn't a foul.
Watch: Referee reverses decision after Gregoritsch's sportsmanship
