The Nigerian was sent off for a second offence, as the visitors fell to a late defeat in a 5-goal thriller.
Onyedika had entered the game in good form, having recently been voted Brugge’s Player of the Month, for his impressive performances in the Pro League Champions playoffs in April.
However, Thursday’s match took a turn for the worse when he received his marching orders an hour into the game against Fiorentina.
Vanaken expressed mixed feelings about the outcome of the match, particularly lamenting the impact of Onyedika’s red card on their chances.
“I have mixed feelings about that late third goal for the Italians. Especially after the red card for Onyedika, you realize that it will be a matter of survival,” Vanaken said after the game.
“And for a long time it looked like we would succeed, but then you still get that late goal in extremes and that is always sour of course.”
He added: “The red card for Onyedika was avoidable, because at that place on the pitch you don’t have to tackle like that.
“By the way, I don’t know if he knew he had already run into yellow.”