A sales prediction made just two weeks ago has proven too optimistic for

Advanced Micro Devices

(AMD) - Get Report

, which Wednesday took the numbers down further.

The microprocessor maker said it now expects sales of $600 million in its second quarter, lower than the $620 million to $700 million it forecast on June 18 and well off the $900 million it was once expected to post in the period. The company cited weak PC sales in making the June 18 forecast, at which time it also said it would lose money on an operating basis during the quarter.

Advanced Micro's shares were off 13.6% at $7.60 in thin premarket trading on Instinet.

AMD's larger rival


(INTC) - Get Report

was also forced to lower its sales outlook last month, saying it expects revenue of $6.2 to $6.5 billion, compared with a forecast in April of $6.4 billion to $7.0 billion.