A 4-0 second-leg hammering, saw Spurs lose the tie 4-1 on aggregate.
Ahead of their FA Cup fourth round clash at Aston Villa on Sunday, Postecoglou said: "I know that this is all kind of reactive to last night. Vicario, Romero, Van de Ven, Solanke, Wilson Odobert, Udogie, Maddison, Brennan Johnson, I could go on and on.
"We had 10 missing players last night. If you take seven or eight key players out of a team it has an impact. I know constantly saying it dulls people to it but it's true. The main thing I would take from last night's game was the way we went about it."
He also stated: "I get the pile on at the moment, it’s really easy for people to stick their boots in and question the players but I don’t question.
"We were disappointed last night didn’t go the way we wanted and we didn’t perform at the levels - but that doesn’t define this group of players in my eyes.
“We’ll go out there on Sunday and put out more of a performance that reflects where we’re at. I have a great deal of belief in these players and what they’re going through and how they’re dealing with it."
On another setback for Richarlison, he added: “It’s disappointing for him, he was emotional, he’s worked really hard to get back, it’s another setback we and him have got to deal with."