United head to Stamford Bridge to take on Chelsea in the quarter-finals on Monday with smalling already looking ahead to the semi-finals at Wembley where they will meet City provided they get the job done in Southwest London.
Smalling insists it is a case of exacting revenge on their rivals following last campaign's narrow Premier League defeat which came on the final day of the season.
"When we saw the draw, it was a definitely the case that the prospect of playing City gives us an extra incentive," Smalling tol the Sunday Mirror.
"It's at Wembley as well, so it would be a massive occasion. But we need to make sure we get past Chelsea, which won't be easy.
"It would be the ultimate revenge to beat City to the Premier League title and knock them out of the FA Cup, especially after last year. It would be so sweet."
He added: "It's drilled into everybody at the club to use the disappointment of last season. None of us want that feeling again."