A bullet has been posted to Celtic manager Neil Lennon, just one day after he was attacked on the touchline during a game against Hearts.Police officers were called to Celtic Park on Thursday, and a spokeswoman for Strathclyde Police confirmed they were investigating the incident.

On Wednesday night, police arrested the man who charged at Lennon and attempted to wrestle him to the ground during his side's 3-0 away win over Hearts.

Edinburgh man John Wilson appeared in court on Thursday charged with breach of the peace aggravated by religious prejudice, and assault aggravated by religious prejudice, but he did not enter a plea and was remanded in custody.

Two men, aged 41 and 43, are also being held by police over a separate incident in which parcel bombs were sent to Lennon, lawyer Paul McBride and politician Trish Godman.

The Celtic manager received death threats while playing for Northern Ireland, and was hospitalised after being badly beaten in Glasgow on a night out in September 2008.

Celtic, a predominantly Catholic club, have been locked in a tense battle for the Scottish Premier League title with their Glasgow rivals Rangers, who draw most of their support from the Protestant community.

The rivalry this season has been especially bitter, coming to a head on March 2 when Celtic played host to Rangers in a fiery Scottish Cup clash.

Rangers had three players - Steven Whittaker, Madjid Bougherra and El Hadji Diouf - sent off and the match was punctuated by a heated touchline exchange between Lennon and Rangers assistant boss Ally McCoist after the final whistle.