Robbie Neilson pulled no punches in blaming Aaron Tshibola for Dons' 4-1 defeat to Bradford City on Saturday.
The on-loan Aston Villa midfielder was sent off after just five minutes when he was caught dawdling on the ball on the edge of the penalty area by Nicky Law before bringing the Bradford man down on the edge of the box, leaving referee Scott Oldham no choice but to send him off.
Two goals in the next 15 minutes, from Romain Vincelot and Charlie Wyke put the visitors in charge before Ethan Ebanks-Landell's header on the stroke of half time threatened to make a game of it.
But Wyke's second and a Paul Taylor fourth ensured the scoreline greatly favoured the visitors, no thanks to Tshibola.
"He has caused us to lose the game today and he'll have that on his shoulders," said Neilson afterwards. "That's football. Tish is a young boy but he has to learn from that. He's here to educate himself and improve, but he'll realise you can't do that in those areas against teams who will press you.
"There's not a lot to say about it - three or four minutes into the game we had a man sent off. It was a bad decision for him to turn inside and take touches on the edge of the box. He knows that already, I spoke to him about it. He will be missing for the next few games and that's his punishment.
"But I can't ask any more from the rest of the players. We worked so hard. The disappointing thing is that we gave up two goals from set pieces and one from a deflection. We had 10 men, but these are usually situations we can handle.
"I felt we were in the game for long periods. When you're down to 10 men you have to sit in two banks of four, and try and get a link, which is why we brought Aneke on. And to be honest, with the chances created, we were up there. We created a few and could have scored a few goals.
"But when you're down to 10 men, you need the referee to make the right decisions at the right time and today he didn't."
One positive for Neilson though was the first time he was able to play both Osman Sow and Chuks Aneke as he sought to get something from the game at 2-1.
And he hopes to see more of them as Aneke returns to full fitness.
He said: "They're top players. I hadn't planned to give Chuks that much time, and hopefully we can get him and Osman on the pitch together when we have 11 men. But it was good to see them both together.
"Bradford will be there or thereabouts - they're a top team with a top manager. We're still fighting to get there and there are positives to take: we were down to 10 men for more than 90 minutes."