( CNN) Sen. John McCain announced Friday in a statement that he cannot “in good conscience” vote for the GOP’s latest plan to modernize Obamacare, likely purposing Republicans’ latest effort to repeal and supplant the Affordable Care Act.

“I cannot in good conscience be voting in favour of the Graham-Cassidy proposal, ” the Arizona Republican said in a statement. “I believe we could do better cooperating with each other, Republican and Democrats, and have not yet really tried. Nor could I support it without knowing how much it will cost, how it will( affect) insurance premiums, and how many people will be helped or hurt by it. Without a full CBO score, which won’t be available by the end of the month, we won’t have dependable answers to any of those questions.”

McCain’s “no” vote builds it very likely Republican won’t be allowed to repeal and replace Obamacare before September 30, as Sen. Rand Paul of Kentucky said he would not back international efforts and Sen. Susan Collins of Maine is also expected to vote “no” on the proposal.