The scar is thick and stretches from the inner part of Anfernee Jennings' knee down through his calf.

It's an unusual spot for a post-surgery scar, but that's because this wasn't a normal injury or surgery.

For those who know the full extent of the Alabama defensive star's Sugar Bowl injury, it's amazing he's already back and ready to play when the Crimson Tide opens its season against Louisville Saturday night.

Until now, all that was known publicly is that Jennings had a knee injury and underwent surgery. It was far from that simple, though.

This situation could have played out much worse if not for the work of Alabama's medical staff.

And a random fan.

"I don't think people realize how serious of an injury that really was because no one's ever really talked about it," said Richard White, Jennings' high school coach. "It was a scary situation for him, his mom and everyone concerned."

**

If you've seen the slow motion replay, you know that Jennings' leg bent in a way that legs aren't meant to bend.

While chasing a Clemson running back, he was unintentionally leg whipped by a teammate at the exact point he had planted his left foot in the ground. The leg swung and hit Jennings' left knee with so much force that it pushed the knee backwards to the point that Jennings' leg looked like the left side of a diamond.

Anfernee Jennings injury in slow motion..



Yikes.. pic.twitter.com/MUihMGlMqR — Doug (@showemdougie) January 2, 2018

It was Willis McGahee-level ugly and an unfortunate ending to the best game of the Dadeville native's college career, one he finished with five tackles, a career-high three stops for a loss and a sack.

"I saw (the replay of it) that night after the game and thought to myself, 'Shit, that's a bad injury,'" said Matt Harrison, a former Alabama offensive lineman who was Jennings' high school defensive line coach. "I've been around football the last 25 years, and that was probably the worst knee injury I've seen in a long time."

The initial diagnosis was a PCL injury, but it ended up being much more serious than that.

Alabama, though, may not have figured that out as quickly as they did without the help of that random fan.

The fan tagged Jennings in a tweet of a picture that showed Jennings' knee bent at that disgusting angle. Naturally, Jennings was scared when he saw the picture late that night and immediately sent it to an Alabama athletic trainer who expedited the process of Jennings getting another exam the next morning.

Upon further examination, it was discovered that the pulse in Jennings' leg wasn't as good as it had been the night before. Further testing confirmed that Jennings had suffered artery damage and had a blood clot, which -- if not tended to within a certain period of time -- can put one at serious risk of losing their leg. Fortunately, it was caught early enough and Jennings underwent surgery in Birmingham shortly after Alabama arrived back home from New Orleans the day after the game.

But it easily could have turned out much different. If as little as another eight or 10 hours had gone by without the issue being addressed, it's very possible the leg would have needed to be amputated, doctors told Jennings.

In an instant, a promising football career could have been over.

"Thank God we got on it," Jennings said. "And thank God for that fan, whoever tweeted that picture. It's crazy, but I'm just thankful and just glad to be back out here."

**

Jennings is lucky.

Lucky that this was caught when it was.

Lucky because, even though it was caught early, it's still a complicated surgery where a lot can go wrong.

It all worked out in Jennings' favor, though, setting the stage for him to be able to play well ahead of original expectations. The initial belief was that additional surgeries may be necessary and that it was probably unlikely Jennings would be back for the Louisville game. Instead, the PCL healed without additional surgery and the talented defender has been full go since fall camp began in early August after sitting out the spring. It's a credit to Alabama's standout medical group that was led by Lyle Cain, Jeff Allen, Jeremy Gsell, James Robinson and vascular surgeon Will Harvey.

"It's definitely been a long process and it's been a challenge," Jennings said. "But sometimes we need a challenge, and it challenged me to push even harder and to just be the best version of myself I can be. I can't thank God enough for giving me a chance to continue to play football and just look forward to a great, healthy season."

Having Jennings back is a big deal for Alabama, especially when you factor in that the Tide recently lost two other top outside linebackers to serious knee injuries.

To former Alabama star linebacker Rolando McClain, the 6-foot-3, 265-pound Jennings has some Courtney Upshaw-like characteristics. In his last two games -- last year's Iron Bowl and then the Sugar Bowl against Clemson -- Jennings had 11 combined tackles with 5 1/2 stops for a loss and the sack vs. Clemson.

"That's the meanest (expletive) you're going to see," McClain said of Jennings. "He ain't like an asshole. He's just got like a mean demeanor about him. But he's also way more athletic than Courtney."

It seems like that should still be the case. Jennings has consistently talked about feeling "great" and back to normal in recent months and is considered one of Alabama's clear defensive leaders. He enters the season with high expectations as well-known NFL draft pundits Mel Kiper Jr. and Dane Brugler both have him ranked as a top-25 draft prospect.

That scar, though, is a constant reminder of the scary journey to get back to this point. A reminder that his football dreams could have been extinguished had it not been for that random fan on Twitter and the quick reaction of Alabama doctors.

"I was worried early on that he may not be able to play again," Harrison said. "But it turned out OK. And for him to, right now, be able to participate and for there to not be any question about whether he's going to play in that first game or not, it's a testimony to the medical staff at Alabama."