The incident occurred less than half-an-hour into the crucial Group H clash at Old Trafford, with the two midfielders going head-to-head off the ball.
As the pair faced off, Fred clearly moved his head into that of his opponent, in similar fashion to that which saw Arsenal winger Nicolas Pepe sent off for a headbutt on Leeds United’s Ezgjan Alioski in the Premier League only last month.
Referee Daniele Orsato did not appear to see the incident in real-time, but was summoned by VAR officials to consult the pitch side monitor.
The writing appeared to be on the wall for Fred, and with United already trailing 1-0 thanks to Neymar’s early goal, Ole Gunnar Solskjaer’s men would have been facing an uphill task to secure knockout qualification.
Remarkably, however, Orsato re-entered the playing field and brandished only a yellow card, leaving PSG manager Thomas Tuchel incensed on the touchline.