An emergency surgery for Sen. John McCain (R-AZ) will force Senate Republicans to delay the health care vote that had been expected to take place on Tuesday.

McCain’s office announced Saturday night he would have surgery to remove a blood clot above his left eye. “On the advice of his doctors, Senator McCain will be recovering in Arizona next week,” the statement read.

McCain’s personal health issue put the vote at risk, in part because Republicans had such narrow margins to move the revised Better Care Reconciliation Act forward. McConnell can lose only two of the 52 Senate Republicans and still advance the bill. Two of them — Sens. Susan Collins (R-ME) and Rand Paul (R-KY) — have already said they would vote to block the bill. McCain’s absence makes it impossible for leadership to have enough votes to start debate on the legislation.

Senate Majority Leader Mitch McConnell said soon after McCain’s announcement that the health care vote would be deferred until McCain can return to the Senate.

It is the second time the Republican bid to repeal and replace Obamacare has been thrown into doubt by a health emergency. Rep. Jason Chaffetz (R-UT) had an unexpected foot surgery in late April, shortly before an expected vote on the House bill. He did rush back to Washington in time to vote for the legislation.