The 2023–24 LEN Euro Cup knockout stage details the matches played to decide the teams that made the final four of the tournament.
The knockout phase involves 16 teams: the eight teams which qualified as winners and runners-ups of each of the four groups in the group stage, and the eight third and fourth placed teams from the Champions League group stage.
The draw took place in Barcelona on 15 December 2023.
The teams were split into two draws, one containing the four teams who finished fourth in the Champions League group stage, who would be pitted up against a Euro Cup group winner.
The other half of the draw would see the third place teams from the Champions League group stage be drawn against a runner up of the Euro Cup group stage.