Hefner is yet to decide if he will undergo the surgery, and will seek a second opinion.
Update - 9:54 a.m.: Hefner will see Dr. James Andrews on Monday for a second opinion on Tommy John Surgery. (Carig, Newsday)
9:59 a.m.: He will also need bone spurs removed. (Castillo, Star-Ledger)
Recovery time for Tommy John surgery is roughly one year, so the surgery would likely knock him out for all of the 2014 season.
According to MetsBlog contributor Chris Walendin, Hefner still has an option left, so, "the Mets retain the flexibility to work him back as needed in 2015," if they choose to retain him.