By Mike Dunn

PHILADELPHIA (CBS) - It’s not over until it’s over – and that’s very true at City Hall. The Council President Darrell Clarke says the budget deal, given preliminary approval last week, may be changed yet again when Council meets Thursday.

Clarke emerged from a closed door meeting with Mayor Nutter and made clear to reporters that the budget deal approved last week over the mayor’s objections will likely be tweaked Thursday, delaying final passage by one week.

“We may have to make some adjustments to the budget, and that will require that we lay over a week.”

Council, last week, rejected Nutter’s plan to switch to a new property assessment system this year. The members voted to delay it one year, and they reduced proposed new money for the school district from $94 million down to $40 million. Nutter, after his meeting with Clarke, said the new system must happen.

“I think its not an ‘if’ question. It’s really more of a ‘when,’ and we’re working on the ‘when,’” said Nutter.

Nutter argues that delaying the new assessment system could open the door to widespread property tax appeals, costing the city, according to his aides, upwards of $100 million in tax revenue. But council members and other critics argued that it would be difficult to vote on new tax rates until the new assessments are complete, and that won’t come until late summer.

Half of the new $40 million earmarked for the schools would come through a hike in a separate tax that affects commercial property owners. But support for that may be waning, and some on council are now questioning whether that portion of the budget package will survive on final passage.