It was a new low for United in what is turning out to be their worst ever season in the Premier League as distress on the pitch is exacerbated by the uncertainty surrounding Louis Van Gaal’s future off it.
“It was a performance that wasn’t acceptable,” he said.
“We need to start rewarding these fans who travel this far and give us great support throughout the whole game. I think we all know that it wasn’t good enough.
“Conceding before half time didn’t help, we didn’t really kick on with that belief in the second half, and I think we lost far too many tackles and a lot of second balls.”
United travel to Shrewsbury in the FA Cup on Monday night and Smalling warned the League One outfit would be encouraged by what they saw on Thursday.
“I think in these games when you play teams that are lesser than Manchester United, you need to win your tackles and second balls,” Smalling said of United’s defeat against Midtjylland.
“When you don’t do that, then it is an even playing field on the pitch. So I think that we’ve only got ourselves to blame for the result.”