Granit Xhaka opened the scoring at the Emirates after 12 minutes with a long-range effort, before Pierre-Emerick Aubameyang sealed the points with a penalty in the second half.
De Gea was the target of criticism for failing to get near Xhaka’s strike, but former Leeds, Tottenham, Blackburn and Burnley stopper Robinson explained that the movement of the ball left the Spaniard with little chance.
“It’s a really wicked swerve on the ball,” he told Sky Sports.
“You can analyse any goal and say there’s a mistake, but this isn’t too much of that.
“For me to start, with he is too deep and far back on his line. You can see on the replay he moves to his left and his feet aren’t in contact with the ground.
“Goalkeepers have a split second once someone has hit the ball. You train every day to predict where the ball is going. His initial first step was towards the flight of the ball.
“The ball really swerved and what he did is take an extra step to go even further.
"As he's taken that, his feet aren’t in contact with the ground so when it’s swerved it stops him from getting back to the other side. That’s what makes it look as bad as it is.”
He added: “The points he’s saved for Manchester United over the years and the games that he’s won, he’s allowed the odd one that slips in.
“It’s probably an error of judgement and there is an element of bad luck in there. We are comparing him to the level he has set which has been very high over the last few seasons.”
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