Mario Balotelli has stuck the knife into Manchester United after the former Manchester City striker mocked their bitter rivals on Instagram following Sunday's derby defeat.

City claimed a comfortable 3-1 win over Jose Mourinho's side with David Silva, Sergio Aguero and Ilkay Gundogan netting for the Premier League champions.

Balotelli, who played for City between 2010 and 2013, took to Instagram to mock United after the game and reaffirm his allegiance for the blue side of Manchester.

Mario Balotelli has stuck the knife into Manchester United after their derby defeat on Sunday

The Italian commented on City's Instagram post of goal scoring hero Aguero to troll United

The Italian, who currently plays for Nice in France's Ligue 1, commented on City's Instagram post of goal scoring hero Aguero.

He wrote: 'Once a blue always a blue!!! Man Utd LOL AGAIN AND AGAIN!'

During his time at the Etihad Stadium, Balotelli was at the centre of one of the most famous moments in recent Manchester derby history.

He scored in City's sensational a 6-1 victory at Old Trafford in 2011 - before revealing the message 'Why Always Me?' underneath his shirt.

Balotelli was at the centre of one of the most famous moments in Manchester derby history

David Silva, Aguero and Ilkay Gundogan (above) all netted for the Premier League champions

The 28-year-old has failed to find the back of the net in seven appearances for Nice so far this season.

Balotelli was once again been left out of the Italy squad last week, this time for matches against Portugal and the United States.

He was included in Roberto Mancini's first two squads as coach and played his first matches for Italy since the 2014 World Cup, but the forward was left out last month and has again been excluded.