The news comes less than a month after a Shard spokesman refuted claims that the UK's would-be tallest tower had hit the rocks (Renzo's backers rubbish rumours of delay to Shard).
This is believed to be due to the credit squeeze affecting international money markets.
The Syrian-born billionaire has been approached by a Middle Eastern backer, who has given Halabi 10 days to decide whether or not to sell his share.
Sten Morstedt, chief executive of CLS, one of the other partners behind the £400 million project, said: 'The banks don't want to have him in. He has got an offer from a third party to buy shares, and he must decide within 10 days whether to accept.'
Piano's skyscraper is probably the most high-profile development to be hit by the global credit squeeze.
The scaffolding is already in place to demolish the existing Southwark Towers on the Shard's site, but any work is unlikely to start until the financing issues have been dealt with.
It was originally hoped that the building would open by mid-2011, but it is now not expected to open its doors until at least 2012.