A bullet addressed to Neil Lennon has been sent to Celtic's home ground, sources at the club have told Sky News.
Police are investigating the parcel, which was delivered to the Celtic Park stadium.
It comes after a 26-year-old man was charged over an attack on the Celtic boss during a Clydesdale Bank Premier League game against Hearts at Tynecastle last night.
A fan clambered from the Hearts section of the main stand onto the pitch and charged towards Lennon, who was on the touchline shortly after his team's second goal.
He aimed a punch at the manager before security officials stepped in and he was taken away by police at the Edinburgh stadium.
The man charged over the attack is due to appear before Edinburgh Sheriff Court.
Strathclyde Police previously said they had detained two men, aged 41 and 43, over parcel bombs sent to the Celtic manager and two other high-profile fans of the club in March.
And last night's attack has prompted questions as to whether it is the latest in a series of sectarian incidents to have plagued Celtic and their manager.
Lothian and Borders Police said Lennon's attacker has been reported to the Procurator Fiscal and will appear in court.
The 39-year-old manager said on his Twitter page after the match: "Don't let what happened to me tonight take the shine off a wonderful team performance... I don't walk alone."
As well as being sent two parcel bombs, Lennon has suffered death threats in the past.
Scotland's First Minister Alex Salmond said: "This sort of behaviour is utterly unacceptable... We cannot have the safety of individuals endangered by such mindless incidents, and our national game tarnished."
Celtic assistant manager Johan Mjallby told Sky Sports 1 HD that Lennon was "shaken" by the latest incident.
He said: "What has happened to Neil is a dark day for Scottish football and I've never seen anything like it. He is shaken but okay."
Police are investigating the parcel, which was delivered to the Celtic Park stadium.
It comes after a 26-year-old man was charged over an attack on the Celtic boss during a Clydesdale Bank Premier League game against Hearts at Tynecastle last night.
A fan clambered from the Hearts section of the main stand onto the pitch and charged towards Lennon, who was on the touchline shortly after his team's second goal.
He aimed a punch at the manager before security officials stepped in and he was taken away by police at the Edinburgh stadium.
The man charged over the attack is due to appear before Edinburgh Sheriff Court.
Strathclyde Police previously said they had detained two men, aged 41 and 43, over parcel bombs sent to the Celtic manager and two other high-profile fans of the club in March.
And last night's attack has prompted questions as to whether it is the latest in a series of sectarian incidents to have plagued Celtic and their manager.
Lothian and Borders Police said Lennon's attacker has been reported to the Procurator Fiscal and will appear in court.
The 39-year-old manager said on his Twitter page after the match: "Don't let what happened to me tonight take the shine off a wonderful team performance... I don't walk alone."
As well as being sent two parcel bombs, Lennon has suffered death threats in the past.
Scotland's First Minister Alex Salmond said: "This sort of behaviour is utterly unacceptable... We cannot have the safety of individuals endangered by such mindless incidents, and our national game tarnished."
Celtic assistant manager Johan Mjallby told Sky Sports 1 HD that Lennon was "shaken" by the latest incident.
He said: "What has happened to Neil is a dark day for Scottish football and I've never seen anything like it. He is shaken but okay."