Celtic lost their opening games to Real Betis and Bayer Leverkusen before beating the Hungarians 2-0 in Glasgow.
They lie third, four points behind the leading two, going into Thursday’s reverse fixture in Budapest.
“Losing our first two games made it difficult, but we knew that we had to beat Ferencvaros,” Postecoglou said.
“We’ve got a chance – that’s kind of where we are at the moment. We’ve got to go for the win.”
There will be no Celtic fans in Ferencvaros Stadion after the Glasgow club were informed that the timescale for implementing a plan to allow entry to those travelling to Budapest with UK vaccine passports was too short.
“It’s disappointing for our supporters and for the atmosphere, but it’s the world we live in,” Postecoglou said. “We will be facing a side with the crowd behind them who have to win and we expect them to put us under pressure.
“We watched them against Leverkusen and Betis and they are a fantastic team with good players and every time you play in Europe away from home it is a challenge.”
Postecoglou does not view the Europa League campaign as a distraction after his side fell four points behind reigning champions Rangers after being held to a 0-0 draw at home to Livingston on Saturday.
“We’ve built a new team, we’re trying to play a certain way, we’re fitting in new players – you don’t want to miss these opportunities to test yourself and get growth and development,” he said.
While Celtic’s run of five straight wins was ended on Saturday, Ferencvaros were winning 2-0 away to Gyirmot and remain one point behind Kisvarda at the top of the Hungarian top flight with a game in hand.
Celtic will be without Carl Starfelt until after the international break, missing two games, after the Swedish centre-back picked up a hamstring injury during Saturday’s draw with Livingston.
Christopher Jullien will not be available to replace him as, although Postecoglou said the Frenchman is “not far away” as he continues his recovery from surgery, he is “nowhere near ready for a game like this”.
The manager pointed out they have options in central defence as Stephen Welsh “has been raring to go”, while Israel international Nir Bitton has often dropped back from midfield.
What did we learn about Ferencvaros last time?
The Hungarian side kept Celtic at bay for 45 minutes in Glasgow but were overwhelmed in the second half.
They have no points from the first three rounds of fixtures and defeat would effectively end their European ambitions for the season.
However, they ran Bayer Leverkusen and Real Betis close in their opening two Group G defeats and have played only one home game in the group so far.
What they said
Ferencvaros head coach Peter Stoger: “We have to be aggressive, we have to attack. We know that we need the points to retain any chance of qualifying.
“We have performed well in our matches so far and there were things we did well in the away game, but we need to avoid the same mistakes and we need to put more pressure on our opponents this time. We need to focus on defence because Celtic is very strong in attack.”
Celtic right-back Anthony Ralston: “We’re all looking forward to it and feeling good as a team.
“It was a good result last time against them, but it is going to be a different game away from home, but we just focus on ourselves and how we want to play and we’re confident as a group that will be enough over there.”
Celtic travel to Hungary for a major European encounter for only the fifth time and for the first since September 1988 – a 1-0 defeat by Budapest Honved. They have won only one of their previous four trips, losing three, beating Ujpest 2-1 in March 1972 in the European Cup quarter-finals.
Ferencvaros have lost each of their past six matches in Europe after a five-game winning start to their campaign in July and August. This is their longest-ever sequence of continental defeats.
The Hungarian side have played four home matches in the Europa League and are still waiting for their first win, losing twice.
Celtic have lost each of their past three away games in the Europa League, conceding four times in each match. They have never lost four games in a row on the road in the competition.
Celtic winger Jota has played a part in 25 open-play sequences that have ended with a shot attempt, the most of any player in the Europa League this season.