After attack, a bullet in the post for Celtic boss Neil Lennon

The Celtic manager Neil Lennon was the target of another death threat yesterday when a package addressed to him containing a bullet was sent to his football club's ground.

Strathclyde Police said they were investigating a suspicious package at Parkhead, and the club's chief executive, Peter Lawwell, confirmed a package which contained "ammunition" had been received.

The incident came the day after Lennon, 39, was attacked by a Hearts fan during a Scottish Premier League game on Wednesday evening. The manager, who has had to live with round-the-clock security after past death threats, was said to be "shaken" after the incident.

The man ran at Lennon after leaping over the barrier from the Hearts section of the crowd. He was restrained by security staff after appearing to swing a punch and missing.

John Wilson, 26, from Edinburgh, was charged with breach of the peace aggravated by religious prejudice and assault aggravated by religious prejudice after appearing at Edinburgh Sheriff Court yesterday.

Lennon and his fiancée, Irene, were reportedly on the receiving end of sectarian abuse while on a night out earlier this year.

Mr Lawwell said the attack on Lennon "highlights the fact that Scottish society must address fundamental and serious issues which lead to outrages of this kind", adding that a further seven people had been arrested at Celtic's training ground following an alleged firearms incident.

Hearts said it would give its full co-operation to the authorities during the investigation into the incident. Lennon has been the subject of a number of attacks and threats during his career, which have intensified since he took on the managerial role at the Parkhead club in June 2010.

Two men were being held yesterday in connection with an investigation into parcel bombs sent to Lennon and to two high-profile supporters of the club in March. The men, aged 41 and 43, were detained under the Explosives Substances Act 1883 after officers searched a number of properties in Kilwinning, Ayrshire.

A package of bullets addressed to the manager were also intercepted at a sorting office in Mallusk, Co Antrim, in January. Two months later, Lennon was involved in heated exchanges with Rangers player El-Hadji Diouf and assistant manager Ally McCoist during an ill-tempered Old Firm cup game played on 2 March.

On 19 April, it emerged that Royal Mail had intercepted two "viable" parcel bombs addressed to Lennon. In September 2008, he was treated in hospital after being attacked in Glasgow's Ashton Lane hours after the opening Old Firm game of the season in which Lennon was the Celtic first-team coach.

"The basic root of this problem is part of the religious and immigration history of Scotland," said Professor Tom Devine of Edinburgh University. "In the 19th and early 20th century there was significant numbers of Catholic and Protestant immigration from the north of Ireland. There was a sense of animosity at that group arriving at the time, and almost a sense of Scottish society being overwhelmed.

"Animosity in working-class neighbourhoods between Catholics and Protestants is weaker than it was in the old days but something of the folk memory still fuels low-level bigotry.

"[Neil Lennon] has got all the ingredients – he is Roman Catholic, he is from Northern Ireland, he is a former Celtic player and now a Celtic manager. He is also seen by Rangers fans as abrasive and unlike past Celtic managers he is very outspoken against anyone who attacks his club. None of this can possibly excuse what he and his family have had to suffer."

Scotland's First Minister Alex Salmond called the incident "utterly unacceptable". "We cannot have the safety of individuals endangered by such mindless incidents, and our national game tarnished," he said.

Neil Lennon: 11 years as a hate figure

As a player, Neil Lennon was often the pantomime villain on the field, booed by the opposition fans.

He has found himself the target of threats and attacks since joining Celtic as a player 11 years ago. In so doing he entered the one arena outside of Ireland where Catholic-Protestant sectarianism is alive and well: Scottish football. Rivalry between the "Old Firm" rivals Celtic and Rangers dates back hundreds of years to waves of immigration from Ireland from both Catholics and Protestants.

Animosity between the two communities still exists at a low level in some parts of Scotland, and some contend that as an Irish Catholic who is now at the helm of Celtic, Lennon was bound to attract attention from extreme sectarian elements.

Others point to Lennon's sometimes abrasive personality as a cause for hatred, noting that many Catholics have played for Rangers in the past and not faced the same ire.

Born in Lurgan, County Armagh, Lennon grew up supporting Celtic. He began to receive serious threats soon after he started playing for them in 2000. Shortly before his first game for Northern Ireland after signing for Celtic, the words "Neil Lennon RIP" appeared on a wall in the town of Lisburn. He was jeered by some of the home support during the game.

In his 2006 autobiography, Lennon said he had expected some "stick" for being a Celtic player playing for Northern Ireland but said nothing prepared him for "the sheer scale of what happened before and during that match". He retired from international football in August 2002 after receiving a death threat, reportedly from a loyalist paramilitary group.

Lennon later admitted the episode left him contemplating his future in football, but he was spurred on by his desire to succeed at Celtic.

In 2003, in Glasgow, two students were fined after Lennon was attacked in his car. A year later, threatening graffiti was daubed outside his home, and he was the victim of road rage on the M8 motorway.

Richard Hall