The fan, wearing a red tracksuit top, evaded security staff as he emerged from the stand behind the benches midway through the second half of the game in Dortmund and made his way towards the Portugal skipper.
Portugal were leading 3-0 in the Group F game at the time, and Ronaldo posed smiling for a photo before the pitch invader ran off trying to escape stewards.
They eventually caught up with him and escorted him away to applause from the stands.
Shortly afterwards, another youngster attempted to copy the first pitch invader but this time an exasperated Ronaldo threw his arms up in frustration and did not agree to a second selfie.
The youth was then brusquely manhandled away from the superstar forward and off the playing area.
