CHARLOTTE, N.C. -- The text came from a Carolina Panthers fan early Friday morning, less than 12 hours after middle linebacker Luke Kuechly went into the concussion protocol for the third time in as many years.

"So, is Luke done for good?" the message read.

Others followed with a similar slant.

Kuechly is only 26, far from retirement age.

But when he walked off the field in the second quarter of Thursday night's 28-23 loss to the Philadelphia Eagles and into the protocol, it raised the question of whether the four-time Pro Bowl selection should consider stepping away for his long-term health.

Professors Eric Nauman and Thomas Talavage, members of the Purdue University Neurotrauma Group that has studied brain changes in athletes since 2009, can't say that should be the first option for the 2013 NFL Defensive Player of the Year.

That's a decision only Kuechly can make, and he has shown no indication that it is a consideration, despite his being in the concussion protocol for three games the past two seasons.

Nauman and Talavage also can't say that retirement shouldn't be an option for Kuechly. But they do have concern for Kuechly's long-term health.

"If nothing else, he should be really, really careful about coming back after this one and really take his time, get much better assessments than are usually given for concussion assessments," Nauman told ESPN.com.

Research has shown that it takes longer to recover after a third concussion than a first or even second one. The Panthers used caution last season when Kuechly suffered his second concussion by holding him out of the final three games.

That decision was made in part to give Kuechly's brain more time to heal and in part because Carolina was out of playoff contention. Coach Ron Rivera said he'll take the same approach this time, making a decision on when Kuechly returns to the field after he clears the protocol.

The difference is the Panthers (4-2) are in the thick of the early playoff picture, leading the NFC South heading into Sunday's game at the Chicago Bears. Kuechly will want to return as quickly as possible -- like he did a year ago. He would have played the final three games last season had Rivera allowed him to.

There also is some debate over whether Kuechly actually suffered a concussion. ESPN's Adam Schefter, per sources, said the team doesn't believe Kuechly did. Rivera would not address Schefter's story, saying only that Kuechly is in the protocol and advancing through the five-step process to return.

Whether Kuechly has or doesn't have a concussion doesn't change that he can't return to the field until he passes all five steps of the league's protocol. Right now, it doesn't look like that will happen in time for Sunday. It doesn't change that Kuechly's health should be the first priority.

Nauman and Talavage would like to see Kuechly fitted with sensors on his skull to monitor the brain activity, as they do with subjects in their biomedical technology.

"They need to look hard at what's happening," Nauman said. "If that was the hardest blow he took that week, he should really be monitored closely, and he might have some hard decisions to make.

"If he took a bunch of big blows, and this one was the straw that broke the camel's back, that might be something you just take a little extra time and you go forward."

That Kuechly, already wearing an experimental device called the Q Collar to help protect against mild brain trauma, played two games in five days could be a factor.

Kuechly didn't take a hard hit to the head when he was removed from Thursday's game. The biggest blow came to his left shoulder, though there was contact with the left side of the helmet.

Talavage cited the case of former Minnesota Twins first baseman Justin Morneau, the 2006 MVP. Morneau suffered a concussion in 2010, when his head struck the knee of Toronto infielder John McDonald while he slid into second base. He missed the rest of the season.

In 2011, Morneau suffered a left shoulder injury that led to mild concussion-like symptoms, and he missed the rest of that season.

He returned to win the 2014 batting title with the Colorado Rockies. Then in 2015, while diving for a ball at first base, Morneau suffered a strained neck and again began experiencing symptoms of a concussion.

He currently is a free agent.

“It essentially got to the point when he was in the field, if he were to dive for a ball, he would essentially get concussed," Talavage said. "It didn't take a blow. It didn't take anything substantial. It just took a sharp dive.

"So at that point, you can make a pretty good argument that Justin Morneau's brain was on the edge. All the networks were connected, but the number of redundant networks were reduced substantially. He could function. He could function in the context of being able [to answer] all the questions, behave normally, but there wasn't a lot of reserve left. It'll be interesting to see in the case of Justin's what happens in the future for him."

Talavage has similar concerns regarding Kuechly.

"Was that blow that he took where he was diagnosed as concussed, did that represent one of the harder hits he took that evening, or had he had earlier in the game a couple of big, nasty blows that may have taken a little time for the effects to be observed?" he said. "Or did those big nasty blows put him right at that edge, and that hit [to the shoulder neck] cause all those networks to just not quite naturally work properly?"

Because of the unknowns, Talavage and Nauman wouldn't be in a rush to put Kuechly back on the field.

"Given that it is his third concussion in three years, one of the things we have found is these changes in the brain usually don't resolve as fast," Nauman said. "So the symptoms might go away in a week. But the actual changes in the brain might take months to resolve.

"I don't know if he necessarily needs to consider retirement yet. What has to be looked at is when is he getting these concussions?"