The guidance reduction comes days after Best Buy rival Circuit City Stores Inc. filed for bankruptcy protection because of eroding vendor confidence, decreased liquidity and the global economic crisis.
The retailer forecast revenue between $43.7 billion and $45.4 billion, as well as a 1 percent decline in same-store sales, or sales at stores open at least 14 months.
Analysts expect earnings of $3.02 per share and sales of $46.23 billion for fiscal 2009, according to a Thomson Reuters survey.
Shares of Best Buy slid $1.72, or 7.2 percent, to $22.16 in morning trading. It has ranged from $20 to $56.01 over the past year.
Best Buy's same-store sales dropped 7.6 percent in October. Same-store sales are a closely watched performance indicator because they measures sales at existing locations rather than newly opened ones.
Chief Executive Brad Anderson said "seismic" changes in consumer behavior have created "the most difficult climate" ever seen by the company.
"Best Buy simply can't adjust fast enough to maintain our earnings momentum for this year," Anderson said in a statement.
Best Buy, which is scheduled to post third-quarter results on Dec. 16, also says the stronger dollar will weaken revenue and profit from its international segment more than previously expected.
Best Buy said that same-store sales between November and February may drop by 5 percent to 15 percent, resulting in an annual same-store sales decline of 1 percent to 8 percent.
Fassler also said increased international exposure is hurting the company, making up about 30 percent of revenue for the third quarter compared with 17 percent in the same quarter a year ago.
"The rapid appreciation in the dollar versus the euro, British pound, and Canadian dollar is pressuring international earnings," Fassler wrote in a client note.
Fassler also said sales in Canada are declining as well.
The overall retail industry is facing what many observers expect to be the weakest holiday season in decades as consumers scale back on spending amid a weak labor market and tighter credit.