Celtic manager Neil Lennon and player Niall McGinn were sent packages containing bullets, it has emerged.
The packages, which were addressed to both men, were intercepted by staff at the Royal Mail sorting office in Mallusk, County Antrim.
The packages, which originated from Northern Ireland, were intended to be delivered to Celtic Football Club in Glasgow.
Police officers were called to the sorting office on January 5 and the items were removed for further examination.
Both men hail from Northern Ireland with winger McGinn a current international.
A spokesman for Celtic said: "It is a police matter and the club has no further comment to make."
Police are investigating and are asking for anyone with information to come forward.
As a player, Lennon received a death threat from Northern Ireland fans after speaking favourably of a united Irish international football team.