On Tuesday, government figures showed that foreign demand for Treasurys fell by the largest amount on record in December.

China cut its holdings by $34.2 billion to $755.4 billion, losing the top spot in terms of foreign ownership of Treasurys to Japan.

Japan also cut exposure, cutting ownership of Treasurys by $11.5 billion to $768.8 billion, a much slower pace than China.

"I am surprised China has not dropped more," Rogers told CNBC.com.

Asked if the US should be worried about this trend, Rogers, who does not hold US Treasurys, said: "Of course. The US should be worried about everyone lightening up – not just China."

The cut in foreign holdings could force the government to make higher interest-rate payments, just as it is struggling with big budget deficits.

Asked if the trend of unloading US government debt was likely to continue, Rogers said: "Probably after this euro scare is over – which may take a good while."

Uncertainty about the size and extent of the euro zone's debt problems weighed on the euro Wednesday, despite a firming of the single currency on Tuesday on optimism that Greece will find ways to cut its deficit.