The Government has already admitted defeat on a key vote following another big Tory mutiny over Europe.
Downing Street indicated it expected the Commons to pass a rebel amendment calling for a real-terms cut in the EU budget.
The prediction came despite frantic efforts by Government whips and David Cameron holding personal meetings with wavering MPs.
Challenged on the issue in the House earlier, the Prime Minister stressed he would prefer a reduction in the EU's seven-year funding package.
But he said he would accept an increase in line with inflation - currently around 2% - as it was the best realistic outcome from next month's summit.
Rebels were quick to play down the intervention from Number 10 - some two hours ahead of the vote on Mark Reckless's amendment.
Backbencher Douglas Carswell said the Government was "managing expectations".
Supporters of the text had previously suggested that the coalition was "within single figures" of defeat.
Declared backers include Mark Pritchard, Zac Goldsmith, Bill Cash, John Redwood, Bernard Jenkin and Peter Bone. Many more could abstain.
Labour MPs have been ordered to vote in favour, and smaller parties are also expected to fall into line.