George Soros' fund has purchased around $2bn of European government bonds previously held by collapsed brokerage MF Global, according to reports.
Key eurozone sovereign debt yields have fallen sharply after successful debt auctions and comments from ECB president Mario Draghi boosted investor confidence.
Eurozone leaders need to act within the next few days or it will be "game over" for the euro, warned Kames Capital's Phil Milburn.
Yields on short-dated Greek debt have hit a fresh eurozone-era high after the country announced a pause in bailout talks with the IMF.
The delay in the US government's efforts to raise its debt ceiling now means it holds less cash on its balance sheet than tech giant Apple.
The US Congress moved one step closer to sealing a deal on its debt ceiling, pushing down yields on 30-year government bonds.
Moody's Investors Service last night said if there is no progress in the US on increasing the country's statutory debt limit, it expects to place that government's rating under review for possible downgrade in the next few weeks.
The US treasury is battling to slash spending after the country's national debt soared to $14trn, reaching a self-imposed limit set by Congress last century.
The UK government borrowed less than expected for the financial year to 1 April, posting a total of £141bn.
Moody's has downgraded Portugal's government debt two more notches because of 'subdued' growth prospects.