The divestment, which the sources said could fetch more than $4 billion, would help Baxter pay down debt following its $10.5 billion acquisition of medical device maker Hill-Rom Holdings in 2021. Baxter had total debt of $16.6 billion as of the end of December.

Private equity firms, including KKR & Co and Carlyle Group, have also expressed interest in the Baxter business, the sources said. Other bidders could still emerge, they added.

The sources requested anonymity because the matter is confidential. Baxter, Thermo Fisher and KKR declined to comment. Celltrion and Carlyle did not immediately respond to requests for comment.

Baxter said in January it was exploring alternatives for its biopharma solutions business and would also spin off its kidney care units.

The Deerfield, Illinois-based company focuses on areas such as critical care, surgical products, nutrition and pharmaceutical equipment.

Baxter's biopharma solutions unit supports drugmakers in the formulation, development and commercialization of drugs typically given by infusion or injection, such as biologics and vaccines.

Thermo Fisher, one of the world's largest suppliers of scientific equipment, has been making acquisitions in recent years to expand its offerings in contract research and manufacturing, including a $5.2 billion purchase of Patheon NV in 2017 and a $17.4 billion takeover of PPD Inc in 2021.

Celltrion, whose co-founder and chairman Seo Jung-jin is South Korea's richest person according to Forbes, is a biopharmaceutical company that also has a contract research and manufacturing arm.

(Reporting by Anirban Sen and David Carnevali in New York; Additional reporting by Chibuike Oguh in New York; Editing by Bill Berkrot)

By Anirban Sen and David Carnevali