In short: No. No it is not. But that isn't stopping people from hitting the panic button this morning, as news of Clay Buchholz's stress fracture surfaces.
Clay Buchholz is a great pitcher, and having him around would be a boost to this Red Sox team. Of this there is no doubt. The thing is, Buchholz hasn't been great for much of 2011. He started out with some control problems and a bout of long ball-itis, and has missed nearly a month-and-a-half with a back injury that will now likely keep him out for the rest of the year. Despite these setbacks, and with far inferior options pitching in his place, the Red Sox are in first place, two games up on the Yankees for the division and 8.5 games up on the Angels for the Wild Card.
The Red Sox have the top offense in the majors, as far ahead of the second-ranked Yankees in True Average as that team is ahead of the fifth-ranked Tigers. They are tied for third in the majors in Defensive Efficiency, a fact that has helped some of their less appealing starters succeed as much as they have. They have the third-best bullpen in the American League according to Fair Run Average (FRA), which separates defensive contributions from a pitcher's actual performance. They just added Erik Bedard to the rotation, and he is a pitcher who, as long as he remains healthy, should be able to put up numbers that would make him the third-best active starter on the team.
Having Buchholz would give this team a formidable four in the playoffs: Jon Lester, Josh Beckett, Buchholz, and Bedard or Lackey as the fourth is a scary rotation even for a team that doesn't hit much. Subtracting Buchholz and putting Bedard in his place, resulting in Lester/Beckett/Bedard/Lackey, is nothing to be ashamed of even if a team's offense and bullpen were average.
The Red Sox are in neither of those situations, though. They have no Buchholz, but they have a potentially historic lineup, an excellent defensive unit, and one of the best bullpens this front office has assembled in their nine years running the team. You will not hear an argument from me that having Buchholz as one of their top three starters in a playoff series would make this team better, but the Red Sox are on a 101-win pace even without very much of the dominating Buchholz we saw in 2010 around. Trim the fat -- i.e., Tim Wakefield, Andrew Miller, and Kyle Weiland -- and this would be an even more talented club. That's the one that will show up in October, and it's going to be a scary roster, with or without Buchholz. Remember that if you start to worry that this season is going downhill thanks to one injury, albeit one to a central figure.