Manchester United are currently trailing 2-0 to Tottenham at Wembley courtesy of Christian Eriksen’s strike and Phil Jones’ own-goal.
In a bid to turn the tide of the game, Jose Mourinho brought Fellaini on in place of the influential Paul Pogba.
However, the Belgian has been hooked just six minutes on from his introduction, with many wondering why.
Yet the answer to the question may lie on the Red Devils’ official Twitter account.
BT Sport commentators were pondering whether Mourinho had ‘done a Nemanja Matic’ when he substituted the Manchester United star.
But it appears Fellaini’s mysterious withdrawal is down to an injury.
“A third and final change for #MUFC: @Fellaini is withdrawn, with @AnderHerrera replacing him,” the club tweeted.
“The Belgian appears to have picked up an injury. #TOTMUN.”
Initially, many thought Mourinho was simply hooking Fellaini because of his poor performance since coming on.
Reports linking him to Besiktas also led some people to think Fellaini had been simply brought on as a sentimental gesture.
Yet that does not seem to be the case.
The game, as it stands, is heading Tottenham’s way.
With Manchester City beating West Brom 2-0 at the Etihad Stadium, the result means United now sit 15 points clear of their noisy neighbours.
And only a huge and sensational collapse will stop the title going to City.