City announced in June they would expand their stadium to accommodate more than 55,000 fans and that work would be completed in time for the start of the next Premier League season.
But Ferdinand queried the decision to add further seats to the ground on Twitter on Tuesday.
Ferdinand, watching City's 1-1 UEFA Champions League draw against Roma, posted: "How many empty seats are there at the city vs Roma game by the way....big CL [Champions League] game & fans would rather Ramsays [sic] Kitchen or something at home.
"Expanding the stadium for what though?? For who though???"
Ferdinand made 455 appearances for United from 2002 to 2014 and won six Premier League titles and the UEFA Champions League in his time at the club.
The 35-year-old now plays for Premier League outfit QPR.
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