DeGrom departed his first start of the season after six innings due to the injury. The decision to scratch him occurred Sunday when the team elected to hold him out of his between-starts bullpen session.
"I would say it's quite a bit better today," deGrom told reporters. "I think we're going to err on the side of caution, though, this early in the season."
Manager Terry Collins said the injury has improved but not enough for deGrom to take his regular turn in the rotation.
It remains possible that deGrom could go on the disabled list.
DeGrom allowed one run against the Philadelphia Phillies in his opening start before exiting.