RIM which was worth more than $148 per share is now trading at $60 due to the U.S. financial crisis and margin pressures caused by launch of new phones to compete with Apple's iPhone.
Microsoft is feeling competitive pressure from Google Inc, which has entered into the world of mobile phone technology, and from Apple Inc, the maker of the popular iPhone.
"RIM is a massive strategic fit" for Microsoft, said Canaccord Adams analyst Peter Misek. "I'm fairly certain they have a standing offer to buy them at $50 (a share)."
If RIM continues to decline to at least $40, a Microsoft bid at $50 would become a premium bid.
Reuters notes that at $60 a share, RIM has a market value of about $34 billion. An offer of $50 a share would value the company at just over $28 billion.