Mejia, who hasn't pitched in the big leagues yet this season, has been dealing with forearm injury issues. He's made six starts in the minor leagues, though none for Las Vegas, and has put up decent numbers at each stop, including an 0.82 ERA in two starts at Binghamton.
Known for being a top pitching prospect for the Amazin's for the last few years, Mejia's stock has fallen since an ill-fated bullpen run in 2010 and a slew of injury issues. In 16 innings as both starter and reliever last season, Mejia was not sharp, posting a 5.63 ERA, striking out 10.8% of batters faced, and walking 12.2% of the hitters he saw. Of course, this is a rather small sample size, and Mejia has never gotten any real burn at the major league level.
There's no word yet on what roster move, if any, will be made to accommodate Mejia on the 25-man roster. If this is to be a one-off performance, Mejia could just take the extra roster spot that teams get in the event of a doubleheader.