Because Jorge Posada is not a big personality to the press — Derek Jeter sucks up all available oxygen, plus Posada isn’t the type — because he wasn’t a hyped prospect, because he has prominent ears and a weak chin, because Joe Girardi-the-player kept him in a subordinate role for at least two years too many, because Joe Torre batted him sixth and seventh and religiously gave him days off, limiting his chances to have big RBI seasons, the Yankees’ catcher’s great value to the team will be made more clear by his absence than it ever was by his presence.

Now that Posada has gone on the disabled list and is absent from the active roster for the first time in almost 12 years, much will be made of his durability. It is typical of the casual disregard of Posada’s contributions to the great success of the Yankees during his career that it would take an injury for his almost uncanny ability to stay in the lineup to be noticed. Since 1999,

Posada has caught more games than any catcher except Jason Kendall (through the end of last season, Kendall had caught 48 more games). Posada, of course, was an order of magnitude more productive than Kendall, whose bat died years ago, as he was more productive than every other catcher during that period, including two players who will sail past him into the Hall of Fame, Mike Piazza and Ivan Rodriguez.

Unnoticed by many, Posada was the secret spine of his team’s success in those years — and though the Yankees have not won a championship since 2000, by any definition they have been hugely successful, with their run of 90- to 100-win seasons and consecutive postseason appearances. During that time, the Yankees have posted the best record in baseball, winning nearly 60% of their games. Generations earlier, Casey Stengel confessed the secret of his own Yankees dynasty, summing it up in one sentence: “I never play a game without my man.” His man was Yogi Berra, who was similar to Posada in perhaps not being the defensive class of the era, but who combined an ability to stay in the lineup, unusual for a catcher, with a terrific bat.

Berra was a prominent part of the Yankees’ offenses, batting fourth on great teams, and he was a popular character, so he won three Most Valuable Player awards — all in seasons that were no better than Posada’s best years.

Posada hasn’t received the same attention, but he served the same function on the Yankees of his time that Berra did on his. He was the dependable presence whose offense, far above average for his position, allowed the team to weather fluctuations at other positions. Paul O’Neill received far more hero worship than Posada. Yet, by 1999, O’Neill was done as a run producer by the standards of right field, and by 2002, he was gone. Two seasons would go by before the Yankees found another regular right fielder, but the Yankees kept winning. In his initial six seasons with the Yankees, Tino Martinez had but one season, 1997, that stood out by the standards of American League first basemen of the day, and sharply declined as the team headed into the new century. Scott Brosius’s bat disappeared and he retired. In 2002, Rondell White had one of the worst seasons by an outfielder in the history of the team. On opening day of the next season, Ken Huckaby sat on Derek Jeter’s shoulder and the team spent the next six weeks watching Enrique Wilson and Erick Almonte play shortstop. Nothing changed. The team kept winning. Posada was still in the lineup.

This is not to say that Posada did it all alone, or that Jeter was at the least an equal partner in helping the Yankees slide past some dubious personnel decisions, severe injuries, and retirements, and of course Posada’s durability was not just dedication, skill, and genetics but good luck. The reason that catchers don’t stay healthy is that they tend to be hit with things — foul tips that break fingers, and sliding base runners that break arms and legs. Posada has suffered the odd muscle strain, and, by his estimation, three or four concussions, but until now he has been able to sidestep the kind of injuries that put Carlton Fisk on the bench for half the season every other year.

Posada visited Dr. James Andrews yesterday, and the Yankees should soon have some clarity as to whether their catcher will be gone for the short or long term. If the latter, they are going to have to try to do something they haven’t done since Girardi was the starter and win without a catcher who can hit — and Girardi was better with the bat than Jose Molina. So far this season, the Yankees have been challenged to hit and pitch consistently. That task now becomes much harder. Without their invisible hero, the struggles of the 2008 Yankees have only just begun.

Mr. Goldman writes the Pinstriped Bible for yesnetwork.com and is the author of “Forging Genius,” a biography of Casey Stengel.