Another bidder may also be interested in the Salix business, they added.

Representatives for Endo and Salix could not immediately be reached for comment.

Representatives for Salix and Actavis could not be immediately reached for comment.

Reuters reported on Monday that Allergan had resumed talks to buy Salix.

It is not clear whether other companies are also preparing bids for Salix.

Reports have said Salix could fetch Valeant as much as $10 billion.

CNBC first reported on Friday that Valeant was close to a deal with Salix.

A spokesman for Salix could not be reached for comment.

A Salix representative was not immediately available to comment.

Allergan declined to comment while a Salix spokesman could not be immediately reached for comment.

The investors include the Los Angeles County Employees Retirement Association and Salix Capital US Inc.

Allergan and Salix declined to comment on the matter.

The bank pension fund, Salix, which owns the building, has invited best offers by that date.

But Allergan dropped its plans when it discovered issues surrounding Salix's inventory levels, Reuters previously reported.

Shire is evaluating how to secure financing for a Salix bid, one of the sources said.

The deal is subject to majority approval by Salix shareholders at a meeting expected later this year.