Toshiba Corp.  (TOSBF)  lurched lower again Friday after Standard & Poor's warned of a potential 'selective default' downgrade for the Japanese conglomerate if it seeks debt financing to assist in its global restructuring.

Toshiba shares fell more than 9% in Tokyo trading to end the session at ¥184 each, extending a decline that began in mid-December -- when the company revealed it would have to book a bigger-than-expected writedown on its U.S. nuclear operations -- to more than 60%. Toshiba said earlier this week that the goodwill impairment would amount to $6.3 billion.