The Argentina international, who has netted 26 goals in 25 games this term, has been absent for the past month with a hamstring injury sustained in the 5-1 demolition of Tottenham, though has resumed full training and could feature at Wembley.
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"First of all, he is one of the best players in the world, and secondly he has a fear factor, and that comes in to play," Kompany told the Manchester Evening News.
"Whenever Sergio is there, we are a better team, but we have had to deal without him for long spells this season and have coped pretty well.
"It goes without saying that when you have a player of his quality that it is pretty special to have him amongst you."
City are gunning for League Cup success for the first time since 1976, when they defeated Newcastle United 2-1 in the final.