The Manchester United star only came on as sub for the last 18 minutes of the 2-2 draw against Arsenal at Old Trafford.
But in that time he was involved in a series of clashes with opponents – with the most bizarre being his ugly tug on Gunners teenager Guendouzi.
The 31-year-old was blown up for a foul but amazingly escaped even a booking from referee Andre Marriner.
And the incident provoked huge emotions on Twitter, with some laughing at the newly-trimmed Belgian and others furious at what they believe is a serious foul.
Some supporters called for the FA to penalise him using video evidence, claiming he should have been sent off for violent conduct.
But others were more amused, suggesting Fellaini was desperate to get some hair back after shaving his famous locks last month.
With ref Marriner appearing to see the incident, it is unclear whether the FA will be able to take any respective action.
But there is a precedent for a player to be banned for hair pulling – with Robert Huth hit by a three game ban for ironically pulling Fellaini's hair.
The incident during United's game against Leicester led to then Reds boss Louis van Gaal blasting Huth with an amazing comment.
He said: "It's not in the books that someone has to grab by the hair and then pull it behind – only in sex masochism."
And football fans were split on whether they saw the incident as funny or out of order.
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