By Phil Mattingly and Lauren Fox

CNN

(CNN) -- Senate Republicans might move forward with a plan to make even deeper cuts to Medicaid than the House's health care bill, which could be a major blow for Senate moderates.

According to Senate Republican aides familiar with the Senate negotiations, leaders in the chamber are weighing lowering the growth rate for the Medicaid program beginning in 2025. Essentially, from that point on, the money states receive for their Medicaid program would be calculated based on standard inflation, the consumer price index for all urban consumers (CPI-U), rather than medical inflation, which is more generous.

One aide stressed that, at this point, no final decisions had been made, but the option was on the table and would be discussed this week as members attempt to coalesce around a final proposal.

If chosen, it would be a small, but significant change from the House bill that could have a major impact on whether moderate lawmakers ultimately vote for the Senate's version of the Obamacare repeal.

While the idea might help convince conservatives like Sens. Ted Cruz of Texas or Mike Lee of Utah to view a final proposal more favorably, it could be problematic for moderates like Portman or Sen. Dean Heller of Nevada, who faces re-election in 2018.

A spokesman told CNN that Portman remains opposed to dropping the growth rate below the level of the House bill, which already would reduce spending on the program by $800 billion over 10 years, and several other more moderate members of the conference have voiced concern over the idea.

Changing the growth rate for Medicaid, however, is only one in a long line of issues that GOP senators are grappling with as they continue to try to bring a bill to the floor as soon as next week.

Portman is playing a key role in another negotiation over Medicaid. Portman has been asking leadership to phase out Medicaid expansion in states like his over a 7-year period, rather than just cutting off federal money for the program in 2020 like the House bill did. According to two GOP aides, however, Portman might not get a win there either. The aides say leadership is leaning toward just a three-year phase out of the program, which is more generous than the House bill, but still less than the seven years that Portman and other Republicans in Medicaid expansion states have requested.