The Yankees are in such bad shape, even the injuries they know about are getting worse. And the possibility of Mark Teixeira undergoing potential season-ending surgery on his injured right wrist is a real one. Teixeira revealed yesterday the injury, which was originally thought to be a strained tendon, is instead a partially torn tendon sheath — which covers the tendon and keeps it in place. General manager Brian Cashman said yesterday there was a 75 percent chance the first baseman wouldn’t go under the knife and surgery would be “the worst-case scenario.” But with the way the Yankees’ luck has been lately, it’s hard to imagine anything else. And while it is similar to what happened to Toronto’s Jose Bautista last year, Bautista also had an unstable tendon which resulted in surgery. Cashman, who spoke with team doctor Chris Ahmad yesterday, said Teixeira’s tendon is stable, which means it is not dislocated. That’s the good news, according to Dr. Michael Hausman, Orthopaedic surgeon and chief of the hand and elbow service at the Icahn School of Medicine at Mount Sinai. “There’s a chance he would need surgery, but more than likely it will go back on its own,” Dr. Hausman said. “It’s not career-ending, but if he waits the full 8-10 weeks and that doesn’t work, it puts him well into the fall.” And with the Yankees already thin at the corner infield positions — actually, just about everywhere — Cashman will continue to look for upgrades. “Wrists you’re always worried about,” manager Joe Girardi said. “We’re not going to rush it. We’re going to rehab and let’s hope it works.”