Speaker Paul Ryan's statement saying he would conference with the Senate on a healthcare bill is not sufficient enough for Sen. John McCain (R-Ariz.)

"I would like to have the kind of assurances he did not provide," McCain told reporters.

The GOP is slated to vote on a "skinny repeal" Thursday night, which would include a repeal of ObamaCare mandates but no replacement measures.

Sens. Lindsey Graham (R-S.C.), Ron Johnson (R-Wis.) and Bill Cassidy (R-La.) held a press conference Thursday afternoon asking for assurances from Ryan (R-Wis.) that the House would not pass the bill without going to conference.

Ryan on Thursday evening offered the assurance but said they wanted a guarantee the House would not seek to just pass the scaled-back Senate bill instead of doing a conference, which could result in the emergence of a broader bill.

"Senators have made clear that this is an effort to keep the process alive, not to make law," Ryan said in a statement. "If moving forward requires a conference committee, that is something the House is willing to do."

Ryan also said he wanted assurances that the Senate would vote first on a conference report. This would ensure the Senate would have to take a potentially tough vote before the House.

Shortly after speaking out against Ryan's statement, Graham and Johnson said they had spoken with Ryan and would vote yes on the bill after all.

It was still unclear how McCain planned to vote. When asked about his vote, McCain declined to tell reporters how he planned to vote.

Leaders want to conference a health bill will the House, hoping they'll be able to churn out a more substantive product.

But moves by the House had raised questions about whether the lower chamber might just approve the Senate bill.

Updated 10:14 p.m. ET