Sen. Thad Cochran will not immediately return to Washington following a four-week absence, raising speculation about the 79-year-old Mississippi Republican’s ability to continue as Appropriations chairman during the remainder of the 115th Congress.

His absence could also have implications for the budget resolution vote this week, though debate was still on track as of Monday, even after Cochran’s office confirmed he would not be present.

Cochran, a seventh-term lawmaker, cast his last vote in the Senate on Sept. 18 and has since been recovering from a “urological issue” in his home state of Mississippi, his office said. His staff had been adamant that Cochran would return to Washington on Monday. But Chief of Staff Brad White announced Monday morning the senator would not return.

“Mrs. Cochran informed me late Saturday night that Senator Cochran has developed another urinary tract infection,” he said in a statement. “After a day of monitoring his condition, and on the advice of his physicians and other health care professionals, Senator Cochran has postponed his return to Washington. He will continue his recuperation at home in Mississippi. The Senator has expressed his intention to return to the Senate when his health permits, and to fulfill his commitment and duties to the people of his state.”

Cochran’s absence means that Republicans are one vote down on the fiscal 2018 budget resolution, a precursor for drafting filibuster-proof tax overhaul legislation. But Maine Sen. Susan Collins’ weekend announcement that she was likely to back the budget plan gives leadership a buffer. Leadership aides on Monday said they did not expect any votes this week to be derailed by Cochran’s absence, including the budget and the $36.5 billion disaster aid supplemental passed by the House last week.

Senate Republican leaders can afford only one defection on the budget vote with Cochran out, and GOP Sens. Rand Paul of Kentucky and John McCain of Arizona have made noises about withholding their support. Last week, Sen. Ted Cruz of Texas said he thought the budget’s proposed net tax cut of $1.5 trillion was too small and the Senate needed to go “much bigger.”

New Jersey absentee?

One wild card was whether Sen. Robert Menendez of New Jersey would be back for votes this week, given that the initial phase of his corruption and bribery trial wrapped last week. U.S. District Court Judge William Walls on Monday refused to dismiss several charges, allowing Menendez’s case to move forward.

While Menendez is not barred from traveling to Washington for votes, the judge’s ruling poses complications for his return. Menendez’s presence in the Senate has been light since his trial began in early September.

If the senator were still absent on final passage of the budget resolution, that would mean GOP leaders could afford Cochran’s missing vote and still lose two more votes on their side, with Vice President Mike Pence breaking the tie. Efforts to reach Menendez’s staff regarding his travel plans were not immediately successful.

In addition, the full Appropriations Committee is scheduled to mark up the fiscal 2018 Interior-Environment and Homeland Security appropriations bills Thursday. Committee spokesman Stephen Worley said it remains to be determined whether the markup session will be canceled. However, the panel announced Monday that subcommittee markups for those two measures, originally scheduled for Tuesday, would be postponed.

If Cochran does not return or cannot continue on as chairman, that would cause considerable changes throughout the committee structure. Cochran was expected to lead the Appropriations Committee and its Defense subcommittee through the end of this Congress.

The next most senior member of the Appropriations panel is Commerce-Justice-Science Subcommittee Chairman Richard C. Shelby of Alabama.

Shelby could potentially sit in for Cochran during markups this week, if the panel decides to continue on as scheduled. Senate appropriators have already reported eight of the 12 fiscal 2018 spending bills, with the ninth and tenth scheduled for this week.

Niels Lesniewski contributed to this report.