The pitch invader ran up to Ronaldo from behind and held him by the throat as he attempted to take a selfie with the 34-year-old.
The fan was immediately dragged away by a steward with Ronaldo appearing to shout ‘Are you crazy?’
Ronaldo had also been targeted by a fan in Juventus’ previous Champions League match, when he managed to narrowly avoid a pitch invader before being they were detained by a steward.
The Portuguese put Juventus ahead in the game after 70 minutes before Gonzalo Higuain completed the victory in stoppage time as the Italian champions advanced to the knockout stages.
Maurizio Sarri’s first-place finish in the group means they could potentially be drawn against Chelsea or Tottenham in the round-of-16.