It looks like he's going to slot in as the fifth starter for the Braves this year. But Minor offers mid-rotation upside, even in his rookie season, because he's already very polished.
One concerning trend that we noted in our write-up of Minor's prospect status is his sudden fly ball proclivity (47.6% flyball rate) upon being called up to the big leagues at the end of last season. So far this spring, Minor's groundout/airout ratio is an amazingly low 0.35. If this trend continues, the young lefty is going to be highly susceptible to the long ball in his rookie season. His 7/4 K/BB ratio in 10 IP is also a cause for concern.
Meanwhile, Brandon Beachy - Minor's competition for the role of fifth starter - has 7 Ks and 0 BBs in 5 innings with a GO/AO ratio of 1.67. It's worth noting that Beachy has been with the "B Squad" and facing weaker competition.
It's also worth noting that fans - particularly fans like me, who aren't scouts - are at a huge information disadvantage in spring training. Maybe Minor's working on some things, and we're not privy to what it is that he's working on. Maybe he's just struggling though. He hasn't surrendered any home runs yet (which has helped him coast to a glossy 0.90 ERA), but at the rate that he's giving up fly balls, he's going to be badly bruised the long ball if this trend does not reverse.
I don't think it's time to discount him yet, but I'd keep him on a short leash as we start the season. Beachy proved himself a competent enough option at the end of 2010.