Cerberus Capital Management, the US private equity firm, is considering a counterbid worth more than $36bn including debt for Equity Office Properties, Sam Zell’s Chicago-based commercial real estate empire, according to people familiar with the matter.

EOP in November agreed to be acquired by Blackstone, a rival buy-out firm, in the largest leveraged buy-out on record. But in recent weeks, there has been speculation on Wall Street that the deal might be vulnerable to a rival offer.

Cerberus declined to comment. The New York-based firm, which last year bought a 51 per cent stake in GMAC, the finance arm of General Motors, and is chaired by John Snow, former Treasury secretary, would most likely not be able to bid for EOP by itself. Other real estate investors including Starwood Capital and Vornado Realty Trust could attempt to join a move by Cerberus, said one EOP shareholder. Starwood and Vornado declined to comment.

A counterbid for EOP would shatter one of the most common practices in the private equity industry, which involves buy-out groups not bidding against each other outside formal auctions.

On Wednesday, EOP shares were up 1.4 per cent at $48.46, close to the $48.50 offered by Blackstone.

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