Mickolio has a 1.50 ERA with 20 strikeouts in 18 innings at Norfolk since being promoted from Double-A Bowie on July 7. The 24-year-old was 2-1 with a 4.70 ERA at Bowie earlier this season.
"We need help in the bullpen, and that's what he'll be," said manager Dave Trembley. "I'm not at liberty to tell you if it'll be in the fifth inning, sixth inning, seventh inning, setup guy, closer, short guy this and that. He's a bullpen guy, so we'll leave it at that."
Mickolio found out about his first big league callup on Tuesday night and admitted that nerves were very much a part of his initial emotions.
"It's very exciting," Mickolio said. "I'm still trying to figure out how to control my emotions right now. Just got done with my first [pitchers' fielding practice] session, so it feels like I got a little bit of the nerves out of the way. But I've still got them."
Mickolio, who attributed the improvement in his numbers from Bowie to Norfolk to mechanical improvements in his delivery, literally, but likely not figuratively, fills Sherrill's spot in the bullpen, bringing his 6-foot-9 frame and unique delivery to the table.
"We kind of thought he'd be here by September if he progressed accordingly," Trembley said of his initial impressions of Mickolio in Spring Training, just after he came over from Seattle with Sherrill and Adam Jones in the Erik Bedard trade. "I think both of our pitching coaches at Double-A and Triple-A did a real nice job with him, and he's a guy that we're glad to have. I'm going to use him.
"He was very good against right-handed hitters. He's got movement. Arm angle is a little different, obviously his size, I think, factors into it, [he has] late life on his pitches. Obviously, he's very excited -- not too many guys from Montana get to come to the big leagues, and he's here for the first time and we're glad to have him."
Amanda Comak is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.