Why wait?

Free agency does not open up until Monday with the NFL’s legal tampering period, but the Giants are making a preemptive strike. They will be visited Sunday by Charles Johnson, the veteran defensive end who spent the first nine years of his career with the Panthers.

Johnson, 29, was released Thursday, which means he does not have to wait to contact or meet with interested teams. The Giants, a bloated $56.5 million under the salary cap, figure to be big spenders once the market opens up and badly need to rebuild their defense. Johnson is a proven player, though he might be on the downside.

Johnson, a Panthers team captain, missed seven games in 2015 with a hamstring injury and managed to get only one sack. Before this past season, he has been a steady, dependable and productive player. His 63.5 career sacks rank second on the Panthers’ all-time list to Julius Peppers (81 sacks with the Panthers).

The Giants this offseason want to add young, talented players. Adding Johnson instantly would add a leader into the locker room. The two starting defensive ends from the second half of last season, Jason Pierre-Paul and Robert Ayers, are both unrestricted free agents.

The Panthers parted ways with Johnson because he was scheduled to count $15 million on the cap and cutting him saved the team $11 million on the cap.