Bruno Lage questioned the referee's decision to send him to the stands following the awarding of an offside goal that contributed to Benfica's Europa League exit on Thursday.
The match officials allowed a crucial Filip Kostic strike to stand in the 36th minute despite the Eintracht Frankfurt wing-back clearly being in an offside position when he bundled home the rebound from Mijat Gacinovic's initial shot.
Frankfurt went on to win 2-0 in front of their own fans, levelling the tie at 4-4 on aggregate and advancing to the semi-finals via the away goals rule.