All season long, the Oklahoma City Thunder have been one of the best defensive teams in the entire NBA. In fact, as of Saturday night, they rank fifth in the league in Defensive Rating (103.1), first in steals per game (9.5) and second in opposing points off turnovers (14.0).Although Paul George can easily be considered a Defensive Player of the Year candidate, Russell Westbrook has been able to focus on the defensive end of the floor and Steven Adams has emerged as a legitimate rim protector, a large portion of OKC's defensive success has been a result of Andre Roberson's elite abilities on that end of the floor.Averaging just 5.0 points and 4.7 assists in 26.7 minutes this season for the Thunder, Roberson is regarded as one of the best on-ball perimeter defenders in the entire NBA, often times being tasked with guarding the opposing team's go-to scorer. Most of what he does doesn't show up in a box score.Now, the Thunder will have to figure out how to replace him.On Saturday, Roberson ruptured his patellar tendon after slipping on the way up for an ally-oop against the Detroit Pistons. Here's how the awful play transpired:As you can see, Roberson was in a lot of pain after his leg bent in an awkward position. After being attended to by medical personnel, his leg was put in an air cast and he was stretchered off the court.

According to ESPN's Adrian Wojnarowski, Roberson will undergo season-ending surgery.

He's certainly a huge loss," Thunder coach Billy Donovan said, per ESPN's Michael Rothstein. "Everyone's been able to see that since he's kinda come back to us and what he's been able to do defensively. And he's found a way to be, offensively, a really effective player for us."

Roberson's importance to his team was highlighted when each member of the starting five had something to say about him after the game.

"It's a hard situation, to kind of be up close and personal with that like that," Carmelo Anthony explained. "The only thing I did was kind of take a knee and pray a little bit and hope things go for the best at that point."

"I'll be there for him along the way, try to help as much as possible, putting him in a good place with the injury," George said. "Because I know how it is. I've been down that road before. So real unfortunate. But one thing about Dre, man, he's tough, and he's a strong person, so he'll definitely persevere through it."

"It's s---, it's real s---," center Steven Adams exclaimed. "He's a huge part of our team and why we win. It's a huge blow to us, but we're just going to have to rely on some of the players to step up."

"A lot changes," Westbrook admitted. "A lot of things that's not seen on the court, a lot of things not seen in the stat sheet -- and that's a huge part. Like I've always said, he's a huge part of our team's success. And obviously, with him going down, we've got to be able to figure out and make up for the things he bring to the game defensively and offensively."

After getting back on the right track recently, the 29-20 Thunder will now have to figure out how to replace Roberson. Rookie Terrance Ferguson as well as Alex Abrines and Josh Huestis figure to see expanded minutes as Donovan adjusts his rotation. It will be intriguing to see if general manager Sam Presti will now make a move ahead of the February 8 deadline.