The Belgium international believes his one-time team-mate will be a dangerous foe at Wembley, while he says the squad must be “hungry” if they are to win
The 26-year-old spent two-and-a-half seasons at the Etihad Stadium, scoring 11 league goals in 73 appearances and claiming winners' medals in both the Premier League and FA Cup, before moving to Wearside in 2012.
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“Johnson is a great player and I think people forget how important he was for us when he was at City,” the Belgian centre-back told the club's official website.
“Many times he made a big impact when he played for us because that's the sort of player he is.
“He will score goals and create chances, and apart from this Sunday, I hope to see him do well in the future.”
City were surprisingly beaten by Wigan in the FA Cup final last season and Kompany, aware that form can go out the window in cup finals, hopes his side can learn from past mistakes and play at their maximum.
“A cup final is a cup final,” the City skipper added.
“It's a one-off game and there isn't any logic other than we have to be as hungry as we have been all season and be at our best on the day - if we are, we'll have a good chance [but] anything else represents a big risk.”