United were stunned 1-0, leaving their Champions League hopes of progress still on a knife edge.
"The second half was up and down," said Blind, who insisted Michael Lang's winner was impossible to defend.
"It was a good cross and he came round the back and I was a little too late. We have enough confidence in the group, we will be well."
United teammate Matteo Darmian argued they turned in a good performance.
"We played well in the first half but did not score. We go back to Manchester with a defeat so we have to recover well."