Manchester City have apologised and launched an investigation after an incident involving Aston Villa goalkeeper Robin Olsen during a pitch invasion by fans of the newly crowned Premier League champions.

City came from two goals down to beat Villa 3-2 on Sunday and clinch the league title in dramatic fashion at the Etihad Stadium.

That led to scenes of jubilation from the home fans at the final whistle, with supporters pouring onto the pitch to celebrate a fourth title in the space of five seasons.

However, Villa manager Steven Gerrard claimed goalkeeper Olsen had been attacked. 

When asked if his players had avoided any harm, Gerrard told reporters: "The answer is no. My goalkeeper was attacked. I think those questions should go to Pep and Manchester City."

Villa reportedly said Olsen was struck on the back of the head, though they were unaware if this was intentional. 

City swiftly issued a statement condemning what they called an "assault".

"Manchester City would like to sincerely apologise to Aston Villa goalkeeper Robin Olsen, who was assaulted after the final whistle at today’s match when fans entered the pitch," the statement read.

"The club has launched an immediate investigation and once identified, the individual responsible will be issued with an indefinite stadium ban."

This incident comes on the back of a spate of pitch invasions up and down the football league in England.

Earlier this week, a Nottingham Forest fan was jailed for assaulting Sheffield United striker Billy Sharp, while on Thursday, Everton fans flooded onto the Goodison Park pitch after their 3-2 comeback win over Crystal Palace sealed Premier League safety.

Palace boss Patrick Vieira was confronted by a supporter while walking across the pitch, and appeared to lash out, seemingly aggravated by the fan's behaviour.