CHARLOTTE, N.C. -- Carolina Panthers linebacker David Mayo didn’t know initially who he was replacing when the coaches screamed for him to get on the field late in the first quarter of Thursday night’s loss to the Philadelphia Eagles.

He didn’t see the shot Pro Bowl middle linebacker Luke Kuechly took to the neck and head area. Since he plays inside and outside linebacker, Mayo could have been entering the game on a key third-down, goal-line situation at either position.

Mayo wasn’t even fully aware Kuechly had entered the concussion protocol for the third time in as many seasons until after the game.

But Mayo is aware now, and he’ll be in the spotlight for the Panthers (4-2) moving forward if Kuechly misses multiple games as he has each of the past two seasons when suffering concussions.

As capable as Mayo might be, statistics show the defense isn’t nearly as effective when the 2013 NFL Defensive Player of the Year is out.

The Panthers are 16-7 the past two seasons when Kuechly has started. They are 5-4 in the nine games he has missed, according to ESPN Stats & Information.

Opponents are averaging 24.2 points when Kuechly is out, 21.4 when he plays. Their success on third-down percentage jumps to 40.6 from 46.7 and sack percentage drops from 7.0 to 5.2.

The numbers after Kuechly left Thursday night with just under six minutes remaining in the second quarter are just as telling.

The Panthers were leading 10-3 when the four-time Pro Bowl selection went to the sideline. They lost 28-23 and at one point trailed 28-16.

Eagles quarterback Carson Wentz threw three touchdown passes when Kuechly wasn’t on the field and none when he was on it. The Panthers had three sacks when Kuechly was on the field and none after he left.

In fairness to Mayo, he didn’t take a physical rep with the first-team defense in preparation for the Eagles. He’ll get those if Kuechly is out for the next game, Oct. 22 at Chicago, and any ensuing games.

But the numbers suggest the defense still will suffer a drop-off.

"He’s a huge leader on this team, on this defense," Mayo said of Kuechly. “A tremendous player, we all know. So it’s huge. He’s well loved and respected in the locker room. Nobody in this locker room wants to see that."

A.J. Klein started three games in 2015 when Kuechly was out with a concussion and the Panthers went 3-0. He started the final six games last season -- three with Kuechly in the concussion protocol and three as a precaution with the Panthers out of playoff contention -- after Kuechly suffered his second concussion in a prime-time game against New Orleans.

The Panthers went 2-4 in those games en route to a 6-10 season.

But Mayo got 21 snaps in the finale to six for Klein and finished tied on the team for tackles with seven in a one-point loss to Tampa Bay. The Panthers felt good enough in the play of the 2015 second-round pick out of Texas State that they let Klein sign with New Orleans in free agency.

Now Mayo is front and center as Kuechly faces another concussion.

"Every week I expect to go in and I prepare that way," Mayo said. “I’ll just be getting more reps in practice, obviously, knowing I’ll be starting the game if Luke is not ready to go."

It won’t be the same, though.

The Eagles capitalized with a 1-yard, game-tying touchdown pass to tight end Zach Ertz a few plays after Kuechly left. Ertz caught a 17-yard touchdown pass in the third quarter to give the Eagles the lead for good.

Kuechly typically plays a big role in covering the tight end, particularly one as high profile as Ertz.

Ertz had no catches on one target when Kuechly was playing. He finished with two catches -- both touchdowns -- on four targets after Kuechly left.

"Some things I’ll definitely have to work on," Mayo said. "Some schematic things, running the defense and making checks and stuff like that. But I’ll learn from the tape and move on."

There were a lot of players praying for Kuechly during a very solemn locker room after the game.

“I love Luke the player. I love Luke as a person, so we’re definitely concerned about his health,” Captain Munnerlyn said. “Hopefully it’s not that bad. Hopefully he can be back with us, but we don’t know.”

Mayo also said he had Kuechly in his prayers.

While many outside the organization have been holding their breath in fear Kuechly would get another concussion, that hasn’t been the case inside the locker room even though Kuechly has been wearing an experimental device called the “Q Collar” in hopes that it would help prevent another concussion.

"We don’t talk about it," Mayo said. "I don’t think anybody is fearful of that. It’s just unfortunate it happened."