A summit of European Union leaders could be rescheduled for five days after the UK's referendum, moving it from its traditional date.
The move would allow leaders to contemplate the outcome of the referendum.
The plan to have the summit on 27 June has been shifted by another day due to the possibility of a Spanish election on 26 June.
So European Council President Donald Tusk has proposed leaders meet on 28-29 June, hoping to get governments to confirm soon.
David Cameron would still be invited to the summit if the UK votes to leave the EU, City A.M. understands.
Leaders have been trying to avoid a clash with any vote, and want time to react to the outcome of the vote before meeting in Brussels.
There are fears that if the UK does vote for Brexit, further divisions could be exposed in the EU, with more countries searching for a reformed relationship with the EU, or even exit.