Nortel Networks' shares fell 20% it revealed it had sought legal advice on a bankruptcy protection filing should its restructuring plan fail.
Its shares are now worth C$0.51 on the Toronto Stock Exchange, valuing what had been Canada's largest corporation at US$194m, compared with about US$250 billion in 2000.
After the dot-com bubble burst, Nortel's recovery was hampered by an accounting scandal and never recovered its former glory before being hit hard again by its biggest customers - most notably Sprint - scaling back their spend on network equipment.
In November, Nortel reported a US$3.4 billion quarterly loss and cut its 2008 outlook, and announce yet more job cuts.