House Majority Leader Steve Scalise’s office said Friday medical treatment will prevent him from returning to Washington until next month, giving House Republicans an even more narrow margin for passing party-line legislation when they return to town next week.

“Last month, Leader Scalise successfully completed induction chemotherapy and had a positive response. It has now been determined he is eligible for an autologous stem cell transplant,” a statement released by his office read. “He is currently undergoing the transplant process, marking a significant milestone in his battle against cancer. Once the procedure is completed, he will be recovering under the supervision of his medical team and will work remotely until returning to Washington next month.”

Scalise, 58, announced in August that he had been diagnosed with multiple myeloma, a type of blood cancer. He returned to the Capitol a few weeks later and was continuing with chemotherapy treatments.

House Republicans were already dealing with a narrow margin for passing legislation after the resignation of former Speaker Kevin McCarthy and the expulsion of Rep. George Santos last month. Scalise’s absence means that if more than two Republicans joined every Democrat, they could defeat a measure.

Another Republican, Rep. Bill Johnson of Ohio, is to resign on Jan. 21 to take a new job.