Tyler Yates has a torn flexor tendon, according to Dr. James Andrews, and will have it examined again in six weeks. It sounds like he won't have surgery, which I guess is good. You can read more about flexor tendon injuries here (and see some rather gross pictures). Without knowing any details of this particular case, it sounds like this wouldn't be that big a deal, in terms of the shape of Yates' career, if Yates weren't such a fringy player to begin with. Andy Pettitte, for example, had surgery to fix a torn flexor tendon in August of 2004 and pitched 222 brilliant innings in 2005. But Yates had an uphill climb back to the majors even before this, and this won't help.
Poor Yates. He just can't stay healthy. It sounds like this is something from which he can recover completely, but at this point he has compiled such a complicated medical record that it will seem amazing if he ever reaches the majors again.