Liverpool suffered an embarrassing 5-0 defeat to City away from home at the Etihad Stadium in the Premier League.
Milner started the game and played for 58 minutes, and the 31-year-old was booed by the City fans.
The former England international was on the books of City from 2010 until 2015, during which time he won the Premier League twice and the FA Cup once.
The former Leeds United and Aston Villa star was not a glamour figure during his time at the Etihad Stadium, but the 31-year-old was always dependable and did his job effectively.
Milner was booed by the City fans on his return to the Etihad Stadium on Saturday afternoon, and former Liverpool and Preston North End striker Mellor, 34, was not impressed.
Don't get why Milner being booed?? What a top pro who has always done well everywhere he been and not the sort of player to cause trouble— Neil Mellor (@NeilMellor33) September 9, 2017