The Moscow financier, best known in Britain as the owner of blogging site Livejournal.com, is said to be plotting a takeover bid for high street bookshop chain Waterstone’s.
Yet if his plans to sell 35 per cent of his 50 per cent stake in Euroset – a sale that would net him up to $1.15bn (£706m) – fall through, his ambitions could be dashed.
Mamut had already built up a 6.1 per cent stake in the company, and is said to be considering a joint bid with the chain’s founder Tim Waterstone.
Reports have also linked him to an investment in Nomos Bank, another Russian initial public offering (IPO) set to price within the coming weeks. Sources had said he could invest the proceeds from his Euroset sale.
Mamut first made a name for himself as the banker behind Russian president Boris Yeltsin’s successful 1996 re-election campaign.
He also holds stakes in several high-profile Russian firms.