The Red Devils went into their clash at home to Atalanta 2-0 down at half time thanks to goals from Mario Pasalic and Merih Demiral.
And it was Demiral's goal, a simple header from an inswinging corner on the right which drove Ronaldo up the wall.
The Portuguese was seen throwing something in his right arm down to the ground as Man United's poor defending gave them a mountain to climb in the second half.
Their poor finishing has also cost them with Marcus Rashford hitting the bar from close range just before half time.
A few minutes before that, Fred curled wide with his right foot but a simple pass across to Ronaldo would have been the better option.
Rashford had his shooting boots on after the break as he pulled one back for the home side following a delightful outside of the boot pass from Bruno Fernandes.
But unless Man United can find another, and ideally two more goals without reply from the Italians, more and more pressure will be heaped on Ole Gunnar Solskjaer.