Joe Mauer, MIN (Bilateral leg weakness)
As more information comes out, we are finding out the true reason for Mauer's weakness: Troy Polamalu tackled him after Mauer made fun of his hair.

Lower extremity weakness can be caused by what seems like a million different things. Neuromuscular fatigue, muscular atrophy, neuromuscular inhibition as a result of knee swelling, herniated discs in the spine, and certain diseases all can produce bilateral leg weakness in the absence of direct trauma to the legs. Since Mauer's condition is severe enough to require a stint on the disabled list, we're sure that if he hasn't already undergone MRI testing, he will be doing so within the next day. Without seeing the images directly, we will discuss the two most likely scenarios.

Mauer could have a large central herniated disc that is causing a narrowing of space for the spinal cord, resulting in pressure exerted directly on the spinal cord (especially if the symptoms in each leg are the same). If the symptoms are not symmetric—such as quad weakness in one leg and calf weakness in the other—then there are likely multiple disc injuries that are placing pressure on the nerve after they have exited the spine.

The intervertebral disc is composed of two types of tissues with different densities and tensile strengths that allow the discs to function the way they do. The outer ring of the disc is called the annulus fibrosis, a thick fibrous ring that keeps the gelatinous nucleus pulposus contained. Think of it as a round banana: the outer skin of the banana is the strong annulus fibrosis, while the edible part is the nucleus pulposus. These intervertebral discs act primarily as a shock absorber and provide a way for the spine to make movements necessary for sports or everyday life.

Intervertebral disc injuries can generally occur in two ways—acutely or through chronic degeneration—but they also seem to have a genetic component. Acute disc herniations can occur from a hyperflexion injury, extreme trauma (such as a motor vehicle accident), or extreme increases of pressure on the disc (as might occur during the lifting of heavy objects). A large portion of the nucleus pulposus can herniate or leak out, putting pressure on the nerves or spinal cord.

Degenerative injuries can also occur over time before a single episode starts producing pain. With degenerative changes, the discs lose their water content and begin thinning, becoming less flexible as a result. The pressures placed upon these particular discs can't be spread as evenly throughout the spine, sometimes resulting in a disc injury between the fourth and fifth vertebrae (or the fifth and the sacrum).

The second scenario entails Mauer not yet being fully recovered from his knee surgery in the offseason. He surely was limited in the amount of impact training he could perform over the winter and during spring training in an attempt to protect the knees. Unfortunately, there is only so much strength training one can do without having to perform those activities.

Our guess, based on Gardenhire's initial conversation with reporters on Thursday, is that Mauer's weakness is the result of a herniated disc. Gardenhire told reporters that Mauer was given Thursday off, but he did not dispense any other information when follow-up questions were asked. The only thing he did admit was that Mauer was sore: he could catch in an emergency, and he was going to be reevaluated on Friday.

Herniated discs do not automatically mean surgery, but they can be devastating to a catcher's career because of the flexion demands on the backstop throughout the game. Depending on the severity of his weakness and what the MRI shows, Mauer will consult with a surgeon to see what, if anything, needs to be done. The difference between the conservative non-surgical route and the surgical route is a rather large one.

For typical rehabilitation without surgery, the total time lost is approximately 60 days in catchers. We lack data on catchers recovering from surgery, but Brad Ausmus missed 100 days in 2010. We will keep you posted with any updates on Mauer's condition and whether he'll require surgery.

Aroldis Chapman, CIN (Arm inflammation)
Whenever Dusty Baker says that a pitcher should be fine in a day or two, we always get a little worried. Chapman's velocity dropped to the mere mortal level of 92 mph—you know, where his "changeup" was in 2010—so he saw the Reds' medical director, Dr. Timothy Kremchek. He was diagnosed with inflammation of the arm, a vague and somewhat unhelpful description. Thanks, doc.

As we have seen and discussed with other players, once something is inflamed, the inflammation doesn't just disappear overnight. If it is truly inflammation—and we have no reason to believe otherwise—it's unlikely that Chapman will return to pitching within a week. There is a chance that he will go on the disabled list, although no one wants to admit that. The value of his arm dictates that they will have to be conservative in this case, so even though good ol' Dusty said he is day-to-day, we would bet on his missing at least a week or two.

New York Yankees bullpen, NYA (Everyone)
That's not as much of a stretch as it sounds like. The Yankees have taken a beating with injuries, and it may not be over yet. Pedro Feliciano was originally diagnosed with a torn rotator cuff, but he actually has a torn capsule in the shoulder that was confirmed by the MR arthrogram.

A torn capsule is more difficult to recover from, as Yankees fans know first hand: the last player with this condition was former Yankee Chien-Ming Wang. If Feliciano decides to undergo surgery—a likely path—he will join fellow left-handed Yankees reliever Damaso Marte on the 60-day DL and be lost for the year. If he wants to give it one last try before surgery, he will undergo PRP injections and refrain from throwing for about six to eight weeks.

Luis Ayala went on the 15-day disabled list with a strained latissimus, a word you have all become familiar with this year. Phil Hughes once again started off a game with decreased velocity, and rumors of his going to the bullpen to “strengthen” his arm are starting to fly. If there is an underlying issue, switching to the bullpen may be the worst thing possible. Hughes has not had velocity even early on in games, so it's not likely that the decline is attributable to fatigue.

Flesh Wounds: Bryan Augenstein went on the 15-day disabled list with a strained right groin, but there is a good chance that he could be out significantly longer than that… Brian Tallet broke his right hand—at least it wasn't his pitching hand—but he did need surgery to put a pin in it, which should keep him out for four to six weeks… Aaron Cook was transferred to the 60-day disabled list, meaning that he won't be eligible to return until late May at the earliest… Robinson Tejeda went on the disabled list after a velocity drop of his own that resulted from inflammation in his shoulder… Chris Young of the Mets had his start pushed back due to right biceps tendinitis, but he may end up making a visit to the disabled list in the near future.