Grobari have also a traditional friendship with Juventude Leonina, the main ultras group of Portuguese side Sporting Clube de Portugal. The direction boards of both clubs have also good relations which was kept ever since the 1955–56 European Cup edition, which on 4 September 1955, in Lisbon's Estádio Nacional, put head-a-head the two teams in what was considered the opening whistle of the UEFA European club competitions. The game finished with a 3–3 draw, with Sporting later losing in Belgrade in the second hand by 5–2, however the club boards of both teams regularly meet from time to time to mark the occasion of this historic event.