MIAMI — Craig Kimbrel struggled with the Mets, making it hardly surprising — his career numbers aside — that he became a roster casualty on Friday, when he was designated for assignment.

Jonah Tong was recalled from Triple-A Syracuse to give the Mets a fresh bullpen arm as they faced the Marlins.

Kimbrel, who turns 38 next week, owned a 6.00 ERA in 14 appearances for the Mets.

In his most recent outing Wednesday, he allowed two earned runs over 2 ²/₃ innings against the Nationals.

The right-hander has earned 440 career saves during a career that could potentially earn him a Hall of Fame plaque.

Manager Carlos Mendoza and president of baseball operations David Stearns informed Kimbrel of the decision after Thursday’s game in Washington.

“[Kimbrel] is such a pro, and we appreciate him and have nothing but respect, and wishing him the best,” Mendoza said. “We’ll see what happens here as he goes through waivers.”

Mendoza said it was made clear to Kimbrel that he would be welcomed back if he’s unclaimed.

“That’s what we told him here; we like being selfish here and would like to keep him around,” Mendoza said. “But also understanding there might be some options for him out there, especially with he way he’s been throwing the ball as of late. What he was able to do the other day, he went three ups, that was something he’s never done before in his career and he bounced back well.”