Former Saints striker Alan Shearer has warned players' lives could be at risk unless the authorities take urgent action to prevent pitch invaders.

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

"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.

"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 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.

"It's completely ridiculous - I can't remember seeing anything as blatant as this."

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.

Shearer added: "There has to be the right message here. Come down like a ton of bricks on Birmingham and punish so-called fans where it hurts, with bans and fines.

"It just proves we have a real problem. The authorities have to stamp it out now."