WASHINGTON — The 2018 National Defense Authorization Act is likely stalled in the Senate until September.

Senate Armed Services Chairman John McCain, R-Ariz., is leaving town to start cancer treatment on Monday, CNN was first to report. He plans to return to Washington at the conclusion of the August recess.

“In accordance with the guidance of his physicians, Senator McCain is returning to Arizona to undergo further treatment at Mayo Clinic,” his office said in a statement Friday. ”On Monday, July 31, he will begin a standard post-surgical regimen of targeted radiation and chemotherapy. During that time, Senator McCain will maintain a work schedule.

After returning to town Tuesday after announcing his cancer diagnosis, McCain had hoped to quickly take up and pass the bill while he was in town, but that plan was upended before dawn Friday on the Senate floor.

Senate Majority Leader Mitch McConnell, on the heels of losing the GOP a pivotal healthcare vote — thanks to McCain’s defection — was poised to take up the National Defense Authorization Act. Then Sen. Rand Paul, R-Ky., objected.

Paul is blocking the bill to get an agreement that would allow votes on his amendments on a war authorization and on indefinite detention.

“Senator Rand Paul requested two bipartisan amendments, one on ending indefinite detention and one on AUMFs. He looks forward to working with leadership and the committee to get this done soon,” said Paul’s spokesman, Sergio Gor.

Without naming Paul, McCain ripped him in a statement on Friday morning.

“It is unfortunate that one senator chose to block consideration of a bill our nation needs right now, the National Defense Authorization Act,” McCain said. “We must uphold our solemn obligation to provide for the common defense and give our men and women in uniform the training, equipment, and resources they need to defend the nation.”

On the flip side, Senate Minority Leader Chuck Schumer, who had objected earlier in the week to pausing the healthcare debate to consider the NDAA, said he was ready for it to advance. McCain and SASC Ranking Member Jack Reed, D-R.I., “arrived at a bipartisan agreement on a list of amendments that can be agreed to, and we can finish this bill,” Schumer said.

Senate Republican leaders said earlier this month that the plan was not to advance the bill without McCain in town and managing it on the floor.