Sources in Glasgow say the investigation is also looking into crazed loyalist plots to kill a MSP and a leading lawyer.
A suspect package was addressed to Mr Lennon on March 4th and police have now revealed it contained a powerful explosive.
It had been reported at the time that the device was a hoax.
Paul McBride QC, a leading lawyer who has represented Neil Lennon, was also sent a bomb.
Strathclyde police has put together a special detective team to track the nail bomber.
A letter bomb was also sent to 70-year-old MSP Trish Godman who wore a Celtic top to the Scottish Parliament on her last day as an MSP ‘as a joke’.
The parcels were all intercepted before they were opened. But a police source said the bombs were all “viable” and added: “They were designed to maim, injure or kill.”
Two packages were addressed to Lennon – one at Celtic Park and the other at the club’s training ground in Lennoxtown.
The package to McBride was addressed to the Faculty of Advocates but was intercepted at a sorting office in Kilwinning, Ayrshire, after a suspicious collection driver reported his concerns about the packet.
It is understood the one to Godman was delivered to her home and had a stamp but had not been processed through the normal mail system. It may have been dropped off by hand.
First Minister Alex Salmond said: “There is a major investigation underway to ensure that those concerned are identified and then brought to book with the full force of the law. We will not tolerate this sortof criminality in Scotland.”