Broker Investec questioned how much the company would be worth if metal prices fail to improve, while pointing to its high debt levels and a need for restructuring.
The note sent shares in embattled commodities trader and miner shed as much as 31 per cent to 66.9p per share.
"If major commodity prices remain at current levels, our analysis implies that, in the absence of substantial restructuring, nearly all the equity value of both Glencore and Anglo American could evaporate," they said.
Investors were also reacting to a cut-price $8m (£5.3m) deal to sell off its Araguaia nickel mine to Aim-listed Horizonte Minerals announced yesterday.
Other FTSE-listed miners were also feeling the heat, with Anglo American and Antofagasta down 7.9 per cent and 4.2 per cent respectively.
Glencore shares are down around 70 per cent so far this year - making it the biggest faller on the FTSE 100.