According to ESPN New York's Adam Rubin, after he was placed on the minor league Disabled List with Triple-A Buffalo, Mets doctors found a small tear in Herrera's left elbow which will require Tommy John surgery, effectively ending his 2012 campaign.
The 27-yr old Herrera had posted a 1.50 ERA in three games for Buffalo so far this season before he hit the DL. In 16 relief appearances with the Mets in 2011 he posted a 1.13 mark.
That leaves the Mets with Garrett Olson, Chuck James -- who are also on the Buffalo staff -- and of course spring training star Josh Edgin as their primary support options to spell Tim Byrdak as a second lefty out of the 'pen. Olson has been used a starter for the Bisons thus far, posting a 2.35 ERA through three starts; he has not surrendered a hit to a lefty this season. In 6.2 relief innings James has yet to allow a run, holding lefties to a .125 mark. And as the closer for Double-A Binghamton Edgin has a 2.08 ERA in five outings.
Additionally, fellow B-Mets lefty Robert Carson has been discussed as another option. Thus far the 23-yr old has a 3.86 ERA with six strikeouts in 4.2 IP for Binghamton. Unfortunately he's also surrendered seven hits, which has been a serious issue for the hefty lefty over the last couple years (see, .299 opponent average in '11, .308 in '10) and at least in my mind takes him out of the running.