* Starboard says Parexel shares "undervalued"
* Parexel considering a sale, Reuters has reported
* Starboard expects significant buyer interest
* Corvex also in the stock, sources say; Jana too - filing (Adds company statement, Corvex and Jana stake information, byline)
By Michael Flaherty
May 11 (Reuters) - Activist investor Starboard Value LP reported a 5.7 percent stake in Parexel International Corp on Thursday, saying the U.S. contract research firm's shares were "undervalued" and represented an attractive investment opportunity.
Starboard is the third activist hedge fund to buy into Parexel's stock and the move places added pressure on Parexel to complete a successful sale of its business to a rival or a private equity firm.
Corvex Management LP, another prominent activist investor, owns a significant stake in Parexel as well, according to people familiar with the matter, and also believes the company should sell itself. Corvex declined to comment.
Jana Partners is the third activist fund invested in the company, owning a $49 million stake as of Dec. 31, according to its quarterly filing. Jana, which is the company's 17th largest shareholder as of last quarter, has yet to speak about the stake publicly.
Parexel said its board and management team is committed to serving the best interests of the company and its shareholders.
"The board and management regularly consider the strategic direction of the company," said Katelyn Villany, a spokeswoman for the company.
Reuters reported on Monday that Parexel, which had a market value of about $3.8 billion as of Wednesday, is pursuing the sale of the company.
Starboard in its filing said there would be "significant strategic and financial buyer interest," referring to rival companies and private equity firm suitors. (bit.ly/2q6bDKd)
The activist move into shares of Parexel comes amid a surge in deal-making across the contract research industry.
INC Research Holdings Inc on Wednesday said it would merge with fellow contract research services provider inVentiv Health Inc in a $4.6 billion deal.
Contract research organizations (CROs), which have benefited in recent years from pharmaceutical companies' drive to cut costs, reduce clinical trial times and expand their research and development presence globally, are exploring opportunities to sell themselves.
William Blair analyst John Kreger said on Monday a sale would be logical for Parexel, adding that the company was struggling to achieve its longer-term revenue targets.
Kreger also said there would be "no shortage" of parties interested in buying Parexel.
The company's shares were marginally higher at $74.81 in afternoon trading on Thursday.
Reporting by Michael Flaherty in New York; Additional reporting by Ankur Banerjee and Divya Grover in Bengaluru; Editing by Savio D'Souza and Lisa Shumaker