SAN FRANCISCO (Reuters) - Microsoft Corp is evaluating its bid for Yahoo Inc because the Internet company may have lost value since it made its offer, a person familiar with the matter said on Friday.

The news, first reported by Reuters, sent Yahoo shares down more than 5 percent in extended trade.

A Yahoo spokeswoman declined to comment. Microsoft was not immediately available for comment.

Yahoo has rejected Microsoft's offer, made on January 31, saying it "substantially undervalues" the company.

The bid initially valued Yahoo at $44.6 billion, but is currently worth about $42 billion.

Source: reuters.com