Elliott's Paul Singer.

Elliott Management Corp. confirmed Monday, May 7, it made a bid for Athenahealth Inc. (ATHN) . 

"Elliott proposes to acquire Athenahealth for $160 per share in cash. We believe we may also be able to substantially improve the proposed price with additional, private diligence," said a letter from Elliott, which was sent to Athenahealth's board on Monday.

The bid tops $7 billion in cash. Last year, Elliott, run by hedge fund manager Paul Singer, bought a 9.2% stake in Athenahealth. Struggling Athenahealth recently made headlines for adding former General Electric (GE - Get Report) CEO Jeff Immelt to its board as chairman

"Athenahealth, as a public company, has not made the changes necessary to enable it to grow as it should and to create the kind of value its shareholders deserve," said Elliott in its letter.

Both Evercore ISI and RBC Capital Markets believe the board of Athenahealth will refuse the initial offer from Elliott due to the proposed $160 per share which is "just above the 52 week high in ATHN shares," RBC said. Athenahealth's 52-week high is $158.66. 

A spokeswoman for Athenahealth wasn't immediately available. 

Athenahealth shares were up 18.6% on Monday to $149.50.