Kemba Walker has historically been among the most durable players in all of basketball. He didn't miss a single game until his third season in the league and had missed a total of only six contests over the past four seasons. When the Boston Celtics signed him to a four-year max contract this offseason, they did so with relative confidence that he would be on the court for most of that time. 

But accidents happen, and that was the case on Friday when Walker suffered an injury that looked scary against the Denver Nuggets. While trying to control a pass that he deflected, Walker ran headfirst into the chest of teammate Semi Ojeleye. Walker was immediately taken off the court on a stretcher. 

Walker was initially diagnosed with "concussion-like symptoms," but the Celtics later diagnosed him with a neck sprain. He missed Boston's game against the Kings on Monday night, but he is listed as probable for the team's game against the Nets in Brooklyn on Wednesday night. 

Due to the fact that the injury was to the head and neck area, the Celtics are obviously going to be cautious in Walker's return to action, and make sure that he is completely recovered before he heads back out on the court. 

"It's always scary. The head injuries, the neck injuries are scary," Celtics coach Brad Stevens said, via the Boston Herald. "And that's the reason he's doubtful, to be honest. I think he could probably play with the strain part but we want to make sure with all the -- with the way he hit, and certainly because of the sensitivity to head injuries." 

Considering how bad this looked on the floor, things could be significantly worse. Stevens went as far as referring to Walker's current condition as a "minor miracle," and he also relayed that Walker is progressing well. 

"Obviously they went through a series of things with the Denver doctors and a series of things when he got back yesterday with our doctors," Stevens said. "And so he is continuing to be monitored in case any of that stuff shows up. But he's been good and he feels good. It's kind of a minor miracle based on what we saw the other day. But the strain is real and he's got some soreness in his back and neck. That's it ... [He's doing] really good. He didn't practice so he went through a number of progressions upstairs on the bike and in the weight room. We're just really lucky it didn't end up being near as bad as [it could have been].  

Head and neck injuries are fairly uncommon in basketball. This play was just a freak accident. Nothing could have prevented it. Thankfully, it does not appear to be serious. 

If it had been, the injury threatened to derail what has been an incredible start to the season for the Celtics. At 11-4, they are currently tied for second place in the Eastern Conference despite already losing Gordon Hayward to an injury earlier in the season. With Hayward slated to return eventually and plenty of trade assets to work with, a healthy Celtics team would have been among the favorites to reach the NBA Finals and potentially win it. 

Walker had been at the center of that. He is Boston's leading scorer at 22.6 points per game, and has made over 39 percent of his 3-point attempts. Further, his decision to sign with the Celtics helped the team get over the free-agent losses of Kyrie Irving and Al Horford. His presence has seemingly led to improved team chemistry, and young players like Jayson Tatum and Jaylen Brown have taken major steps forward by his side. 

But if this injury had indeed kept Walker out for an extended period, it would not have been the first time Boston has suffered this sort of calamity with a star free-agent addition. Hayward suffered a gruesome ankle injury in his very first game with the Celtics. He struggled in his return to the court last season, and now that Boston has spent most of its draft capital and financial flexibility, weathering another long-term storm in terms of injuries could have derailed the team's entire plan for contention over the next few years.