Ronny Deila was labelled a 'traitor' in a stinging banner from the Standard Liege fans who used to idolise him.
The former Celtic manager decided to walk out on the club last week to join deposed Belgian champions Club Brugge despite insisting a few days previously there had been no talks.
Standard were thumped 4-0 at home by Cercle Brugge at the weekend under caretaker boss Geoffrey Valenne and there was chanting against the Norwegian.
And the Standard fans unfurled a banner that stated, 'Deila, you will soon see the treatment we reserve for traitors.'
Valenne admitted their preparation was non-existent with the turmoil of Deila leaving.
He said: "The fans feel betrayed by Ronny. We all do, myself included.
"I am an employee of the club so took the role and we tried to prepare for this match, but what happened made it very difficult.
"It's fair to say the players were not 100 per cent focussed on the match.
"Many players liked the coach. We had to turn the button off overnight. Unfortunately, the players were affected by his departure.
"Ronny was symbolic and charismatic. He took up a lot of space in the dressing room.
"He made his decision and I have to respect it because that's football. But I am very disappointed."
Meanwhile, Ange Postecoglou savoured Celtic’s title party but insisted he needed no reinforcement of what his Parkhead role brings him.
The 57-year-old is reported to be high on Tottenham’s wanted list as they search for a new manager but Postecoglou remains focused on winning the treble with Celtic ahead of next weekend’s Scottish Cup final against Inverness.
Celtic warmed up in style with a 5-0 win over Aberdeen before collecting the cinch Premiership trophy.
“I don’t need any reinforcement, I feel it every day,” Postecoglou said. “I know it’s a special football club and I have had wonderful support from day one.
“I am enjoying it, I love being part of this football club but also I take the responsibility I hold very seriously.
“Days like today are about enjoying them, appreciating the great people I have got around me, the staff and my own family.
“These days are ones where you get the chance to appreciate what you have got. It’s a special day, we do trophy days well.”
