Kompany’s Belgium team were saved by the impact that Fellaini made in their 2-1 victory over Algeria at the World Cup, after the powerful midfielder came off the bench to score and start his nation’s revival.
Belgium had looked out of sorts before Fellaini was introduced to the game, as they fell behind to a resilient Algeria outfit.
The 6ft 4inch midfielder gave them an outlet that they had been desperately lacking and scored an excellent header to bring his side level before Dries Mertens completed the comeback.
And Kompany thinks that his compatriot has been written off too early by many at Old Trafford, feeling that Fellaini can have a similar impact at club level.
"Fellaini is a terrific player and with any player in his first season at a new club, it can be tough,” the commanding City centre-back said.
"You have to grant players a couple of seasons before you can judge someone."
"For us, with Belgium, he has been doing it time and time again."
It was noticeable that Fellaini's role for Belgium was far different to the one he has played for Manchester United in his first season at the club.
He came on and immediately was utilised as a second-striker for his nation, with his presence designed to create spaces and hold the ball up for their enviable attacking talents.
It was a role that he was used to playing at Everton, where he impressed and showed the form that convinced David Moyes to spend £28 million on him when he was in charge at United.
At Old Trafford, however, he was used in a more defensive role and has been expected to provide protection to the backline as well as link the play up with his passing, something which he has looked uncomfortable doing.
This performance, though, may convince new United manager Louis Van Gaal to play him in a more advanced position which he looks far more adept in.
If Fellaini does manage to turn the opinion of the Old Trafford faithful around then it will be a far greater comeback than the one which he inspired his nation to against Algeria, as he has been written off by the majority of the fan-base.