Nunez wasn't available for Wednesday's 8-5 loss to the Diamondbacks due to forearm tightness, Tim Britton of The Athletic reports.
Nunez returned from the injured list Friday after spending nearly a month on the shelf due to a right forearm strain. He went 1.2 innings and struck out three batters during his first appearance back Saturday, but manager Carlos Mendoza said the 28-year-old reliever hasn't recovered properly from the outing and is once again experiencing forearm problems. He's considered day-to-day for now, though the Mets will likely want to take a closer look at him to determine if he'll need to make another trip to the IL.