It was Nottingham Forest's first home European game since 1996, but not the type of result the Australian coach needed, with his team's fragility from set-pieces proving costly.

Forest was twice undone by deliveries into its box in the first half, with Ousmane Diao and Mads Bech on target for the visitors in the space of six minutes.

Dan Ndoye briefly restored parity between those Midtjylland goals, but matters were made worse for the hosts when centre-back Murillo was forced off injured.

Substitute Chris Wood saw two goals disallowed in a matter of minutes as Forest upped the pressure late on, while Elias Olafsson denied Neco Williams and Morgan Gibbs-White, but Midtjylland delivered the knockout blow when Dario Osorio led a blistering counter-attack, with Valdemar Byskov slotting home.

As chants of "sacked in the morning" rang around a rapidly emptying venue, seemingly directed at Postecoglou, Diou was adjudged to have fouled Elliot Anderson in the box after a video assistant referee (VAR) review, handing Forest a reprieve.

Wood sent his penalty calmly down the middle, but it proved too little, too late for Forest, as the pressure grows on Postecoglou.

When asked about the supporters' discontent, Postecoglou said: "I heard [it]. They’re fans. They’re entitled to their opinion and they want to see their team win.

"Nothing surprises me in football anymore."

The Tricky Trees are now winless across all competitions since their opening day victory over Brentford, and have taken just one point from two UEFA Europa League games so far. 

Postecoglou has become Forest’s first permanent boss in a century to go winless in his opening six matches – losing four and drawing two – a feat last matched by John Baynes, who failed to win any of his first seven games in 1925.

Indeed, since Postecoglou took charge of Forest for the first time on 14 September (AEST), it has conceded the most goals, 13, of any Premier League side in all competitions, while it has shipped seven set-piece goals, three more than any other side.

"Really disappointing – really, really poor goals we conceded in the first half, allowing the opposition to get comfortable. It’s the story of our last few games – key moments," Postecoglou said.

"We knew the threat they provided. We haven’t shown the same desire and determination as the opposition in those moments."

Asked if the defeat represented a step back, Postecoglou added: "Progress is us winning games of football and we haven't done that. Yes, our football has been compelling at times but you’ve got to win games of football and that’s what we’ll try to do.

"We’ve got to keep going. There’s no hiding in the sport we’re in. You’ve got to keep your head up, recover, we’ve got a tough game against Newcastle [United] at the weekend."