Pep Guardiola was left shocked by the attack on Aston Villa goalkeeper Robin Olsen on Sunday.
Guardiola’s City claimed the Premier League title at the Etihad Stadium, scoring three times to complete a comeback against Villa.
City needed to win in the end, afer Liverpool came back against Wolves, and three goals in quick succession saw the comeback completed.
There were scenes of celebration at the Etihad Stadium as thousands of fans poured onto the pitch to celebrate the title win.
But City fans were let down by one fan, who assaulted Villa goalkeeper Olsen as he tried to leave the pitch.
It follows incidents during pitch invasions at Everton, Nottingham Forest and Port Vale within the last week.
And Guardiola wasn’t aware the incident had happened when BeIn Sport quizzed him during City’s celebrations.
Unaware of the situation, Guardiola simply said: “I’m so sorry,” before being rushed off to celebrations.
City have said they will issue a lifelong ban to the supporter when they are identified, while police are working with the club to identify the person involved.