Earlier, Conservative MP John Baron indicated that the number of Tory MPs supporting his motion might be smaller that initially expected.
He said that the draft Bill has kept several of them on side.
Cameron has pledged to back a Conservative MP's EU referendum bill, as Cable labelled the move potentially 'damaging' for the country.
114 Conservative backbenchers have voted in favour of a eurosceptic motion to amend the Queen's Speech in defiance of the Prime Minister.
David Cameron has denied he has buckled under pressure from his backbench MPs over the EU debate.