'Mega' cameras captured an image that will cause controversy over the next few days and cast a negative image on an otherwise fabulous sporting spectacle.
Brought on in the 74th minute in place of Olivier Giroud, former Real Madrid man Morata was subjected to numerous chants and cheers by the Barcelona faithful, including: "How bad are you, Morata, how bad are you".
As the match went on, the Spaniard became increasingly frustrated by the reception before he lost his head completely, turning to the home supporters and putting his hand down his crotch.
It was a hugely inappropriate action, showing that the 25-year-old is still extremely immature as he should have expected such a hostile environment given his past affiliations but yet evidently wasn't prepared on how to deal with it.
The scoreline did not help matters, with the tie effectively already decided when Lionel Messi scored Barcelona's third in the 63rd minute to seal a 3-0 victory on the night for 'Los Cules and a 4-1 aggregate win.