We still don't know if Russell Westbrook, who underwent arthroscopic surgery on his right knee on Sept. 12, will be ready for the Thunder's opening-night matchup with the Warriors. But we do know for sure that Westbrook's teammate, Andre Roberson, will not be playing in that game -- or any other game, for that matter, for quite a while. Via ESPN:

Oklahoma City Thunder guard Andre Roberson will miss at least an additional two months after undergoing a procedure Thursday following a setback during his rehab from left knee surgery, a Thunder spokesperson said. After suffering a ruptured patellar tendon in January, Roberson was on track to return to the floor in November, but he needed an additional procedure because a suture was causing irritation that he couldn't play through.

OK, so let's do some math. If Roberson was on track to return in November, even if you take the most optimistic track and say the beginning of November, then two additional months out would keep him out until January. At least. And that's if everything goes as planned from this point forward. To put it mildly, this is terrible news for the Thunder, who in my opinion were set to come into the season as one of the two or three best defensive teams in the league. Without Roberson that forecast changes drastically.

Even casual fans at this point are aware of Roberson's defensive prowess. He's as good as it gets on the perimeter. He can guard 1-4 at an elite level. He can check the best players in the game straight up, no help necessary. He's not the Thunder's best player, but he's the axis on which they swing from merely a good team to a potentially great one. OKC had won seven straight games when he went down last season. With him, they were starting to look like a team capable of beating anyone. Without him, the Thunder barely made the playoffs and then got smoked in the first round by Utah.

Let's look at a few numbers: OKC's starting lineup last season, when it included Roberson, outscored opponents by 14 points per 100 possessions -- which, for context, was more than four points per 100 better than Golden State's starting lineup and almost six points better than the Warriors' dreaded death lineup. Going deeper, last year's OKC team had 13 different four-man, three-man and two-man combinations that boasted a double-digit point differential while playing at least 300 minutes together. Roberson was in 11 of them. According to Cleaning the Glass, OKC's defense gave up almost 12 points fewer per 100 possessions when Roberson was on the floor, which put him in the 99th percentile of defenders -- all of which is just a nerdy way of saying there aren't many players in the league who can lock up the best scorers in the world like this:

That, right there, is the kind of defense you can't teach. And now Roberson is out for an additional two months. You might say: "Who cares about the regular season? As long as he's healthy for the playoffs." I would say to that, you have to make the playoffs first. The West is a guillotine. Neither the Nuggets nor the Lakers made the postseason last season, and both figure to this time around, meaning two playoff teams from last season could well be out. The Grizzlies get Mike Conley back and could threaten for a spot if all goes perfect. That would make three newcomers.

Bottom line, anything short of 50 wins is going to have you biting your nails. You might get in, but it'll be by the skin of your teeth. OKC won 48 games last season. I would've pegged them for 53-55 this season with a healthy Roberson. With this news, however, 50 wins is going to be tough. There's a decent chance they go through these first two months as a .500 team at best. That's a lot of ground to make up. Even if they get in the playoffs (and, yes, I would still bet that they will), now you're talking about something like a six-seed, maybe a five, maybe a seven, but top-four suddenly becomes very tough. That means you're potentially facing a Golden State, or a Utah, or a Houston in the first round rather than going in as a potential top-three seed with home-court advantage.

When you start looking at teams like the Pelicans, Spurs, Lakers, Thunder, there isn't much separating them. What was supposed to separate OKC was its defense, where it doubled down this offseason, failing to add any shooting to a team that already can't shoot a lick outside of Paul George. Westbrook and Dennis Schroder both shot 29 percent from three last season. They were going to hang their hat on stopping people, and hope that Westbrook and George could provide enough offense. Now they'll have to provide even more. From the time Roberson went out to the end of last season, OKC gave up four more points per 100 possessions. That might not sound like a lot if you aren't familiar with NBA metrics, but it's like half-seconds on a 100-yard dash. It's huge.

Granted, they got rid of Carmelo Anthony, so they at least don't have that defensive drain to worry about. George, Steven Adams and Jerami Grant are still super impactful defenders. Westbrook is capable of being a good defender, and it just became high time that he start taking that seriously. Roberson has, to a fairly large degree, put his print on the Thunder by covering for other people. Now he needs them to cover for him. If last year is any indication, there is little evidence that they are prepared to do that.