Matt Harvey has a partially torn UCL in his right elbow. He will likely require Tommy John surgery at some point although the Mets figure to think carefully and reassess the situation in a few weeks to make a final decision. I think it's best for Harvey, the Mets, and anyone who owns Harvey in a dynasty or keeper format for Harvey to get the surgery and recover ASAP. Don't expect anything out of Harvey until 2015 if he does undergo the surgery. Nowadays, pitchers who undergo Tommy John have a much better chance at returning to form post-surgery. Harvey should be fine and effective for 2015 if he does undergo surgery but keep in mind he'll likely be on a strict innings limit.
If he does not end up getting the surgery then he'll be a true wildcard heading into 2014 drafts. The partially torn UCL likely means that he'll require Tommy John at some point in time. The ligament could fully tear at any point. He'll be a huge injury risk for 2014 if he and the Mets decide to rest, rehab, and pitch through this. I think that the possibility of Harvey not getting surgery is unlikely. 2015 was probably going to be the Mets target year to legitimately compete anyway.
With Harvey injured, look for the Mets young pitchers such as Rafael Montero, Noah Syndergaard, and Jenrry Mejia to have a much better chance to spend most of 2014 in the big-league rotation.