The board of the listed Investa Office Fund has cleared the way for its largest shareholder, Investa Commercial Property Fund (ICPF), to vote on Blackstone’s AUD3.1bn (€2bn) takeover offer.

The decision has intensified speculation of a challenge to the Blackstone bid, potentially from Macquarie Real Estate Investment (MREI), which this week bought 50% of the fund management platform of IOF.

At the very least, according to market sources, it looks almost certain that Blackstone will need to increase its offer. By how much will be determined by feedback from large institutional investors, believed to include ICPF, which owns 19.99% of IOF.

Some shareholders are concerned that the offer does not match the value of the trust, which has benefitted from an uplift following revaluation of its office towers.

Its independent expert, KPMG, has described Blackstone’s offer as “not fair but reasonable”.

Investment bankers are suggesting that Blackstone’s offer of AUD5.15 per security might need to be increased to around AUD5.22.

ICPF has not decided how to vote in a unitholders’ meeting called to approve the Blackstone proposal. The meeting has now been postponed from next week to the end of the month, due to the change in dynamics surrounding the bid.

A source said it would be “fantastic” for ICPF to keep IOF and ICPF together. As well as its asset manager, ICPF co-owns some of the office towers in the IOF portfolio.

Sources have previously suggested that some ICPF investors, which are mostly Australian superannuation funds, would back a move on IOF if they consider the acquisition is being made at the right price.

These investors would not be prepared to pay a premium for IOF.

Speculation has arisen that Macquarie itself, an investment bank, could take the lead in making a counter offer.

Macquarie, which is believed not to own any shares in IOF, has a clear strategy to expand its presence in the Australian real estate market.

Macquarie Capital is a joint venture partner with Canada’s Ivanhoé Cambridge in Logos, a fast-growing pan-Asian logistics player.

It has also formed a joint venture with Greystar to build student housing in Australia and Asia.

A source familiar with Macquarie said: “IOF has a good portfolio which is attractive to a wide range of investors.”

The source said Macquarie is not concerned that the Australian office market appears to be at its peak. “It invests through cycles. It is a long-term investor.”

The source said Macquarie intends to help grow the ICPF platform and that Macquarie does not rule out anything, including mergers and acquisitions, to feed growth.

“It will work with ICPF. Ultimately, it is relying on the ICPF management to put in place a business plan setting out its growth strategy.”