Former England striker Alan Shearer has warned that players’ lives could be at risk unless urgent action is taken to prevent pitch invaders as the Professional Footballers’ Association called for a full inquiry.

Aston Villa captain Jack Grealish was punched by a Birmingham fan and Manchester United defender Chris Smalling was confronted on the pitch by an Arsenal supporter in two separate incidents on Sunday.

It followed an episode on Friday in which Rangers captain James Tavernier was challenged by a pitch-invading Hibernian fan in his side’s stormy Scottish Premiership draw.

“It is absolutely disgusting and if we don’t stamp it out now, next time it could be a knife,” Shearer said in his column in the Sun newspaper.

“It’s that serious. Where are we at in football when some thug thinks that is what he is going to do?”

Grealish was assaulted at St Andrew’s by Birmingham fan Paul Mitchell, 27, who was later charged with invading the pitch and assault, while Smalling was confronted in United’s 2-0 defeat to Arsenal at the Emirates Stadium.

“The football authorities have to be seen to nail Birmingham for the behaviour of their fan,” Shearer said.

“If that means docking them points, playing in an empty stadium, so be it. There cannot be a strong enough punishment.”

In a statement read out by the prosecutor at Mitchell’s Birmingham Magistrates’ Court appearance, Grealish said he was fortunate not to have been seriously harmed.

“I cannot help but feel how lucky I was in this incident,” Grealish said.

“It could have been so much worse had the supporter had some sort of weapon.”

Pub worker Mitchell pleaded guilty to assaulting Grealish and also admitted a charge of invading the pitch.

“He cannot explain what came over him yesterday morning. His initial foolish intention was to just go onto the pitch and whip up the crowd,” Mitchell’s solicitor told the court.

Birmingham said Mitchell would be banned for life from St Andrew’s and Arsenal later pledged the same punishment would be imposed on the pitch invader at their match.

A man named as Gary Cooper, 30, was charged with common assault over the Smalling clash, the Metropolitan Police confirmed.

‘Disgraceful, cowardly and criminal’

The FA said the incidents “crossed a line” in terms of fan behaviour and promised to examine security measures at the two matches in question as well as what future steps can be taken.

“Not only is it an offence to enter the pitch, which could result in a club ban and criminal charges for the individual, but it also puts the safety of the players at risk,” read a statement on the FA Spokesperson Twitter account.

“This is entirely unacceptable and we strongly condemn both incidents.

“We will be working with the clubs, the leagues and the police to discuss what collectively needs to be done to protect players and officials on the pitch.”

PFA chief executive Gordon Taylor said the attack on boyhood Villa fan Grealish, who scored the winning goal against Birmingham, was “disgraceful, cowardly and criminal”.

“We have seen an increase in such behaviour at clubs this season. It’s been racist abuse, it’s been anti-Semitism and now it’s real fear for the safety of players,” Taylor told Sky Sports News.

When asked about what sanctions could be implemented, Taylor said: “There’s a combination you can consider – fines, ground closures, playing games behind closed doors and points deductions.”

Meanwhile, Rangers manager Steven Gerrard called on fans to take responsibility for their actions after Tavernier became embroiled in a shoving match with a Hibernian fan who jumped out of the stands to kick the ball away.

“It is a huge concern. For the image of the game, it’s not right at all,” said the former England player.

“Fans have to take responsibility and think before they do these type of things, because if it continues someone is going to get hurt and hurt badly, and no one wants it to get to that stage.”