IWG, the company behind the Regus brand that runs offices in about 3,000 locations in over 1,000 cities, did not disclose any further details about the possible cash offer.
The business had a market capitalization of about 1.8 billion pounds ($2.4 billion) on Friday after stock market trading finished.
IWG said there was no certainty any offer would be made by Onex and Canadian property firm Brookfield.
The approach comes after IWG warned on full-year profit in October, citing a weaker London market and disruption due to natural disasters in the United States. That warning sent its shares tumbling.
The UK property market was one of the most prominent casualties of Britain’s June 2016 vote to leave the European Union, as investors worried financial firms would move jobs to Europe, hurting demand for office property in the capital.
Reporting by Rahul B in Bengaluru, Editing by Louise Heavens and Mark Potter