Francisco said his left oblique area stiffened after he cooled down after that game. He tried to play catch before Saturday's game to test the injured rib area, but the discomfort did not subside.
Manager Terry Collins said Francisco was unavailable to pitch during Saturday's 4-3 loss to the Yankees. Collins was unsure how long the closer may be out.
"I felt a little sore after the game last night, but I thought it was normal," Francisco said. "I put ice on. Today I feel a little worse. I went outside anyway and threw to see if it was something minor. I still feel it."
Francisco said he had not felt irritation during Friday's save -- only afterward.
"After I got cold, I started feeling a little bit sore," he said.
"Wait until tomorrow and see if I feel better," he said. "We'll go day by day."
Francisco, in the first season of a two-year, $12 million deal, has converted 18 of 21 save chances.
His unavailability, whether short-term or lengthier, would be seriously damaging to a bullpen that already owns the highest ERA in the majors at 5.30.
The Mets are only carrying six relievers this weekend, rather than the typical seven. And with Francisco active but unavailable, they really only have five. So they could look to Triple-A Buffalo for help.
Among the logical candidates, Pedro Beato is having the most success. Ramon Ramirez is on a major league rehab assignment for a right hamstring strain with the Bisons, but he and Jenrry Mejia have struggled in relief roles with the Triple-A club.