There may be a reason for Zack Wheeler's struggles with his control during his first two minor league starts.  News broke earlier tonight that Wheeler underwent an MRI to examine a blister on the middle finger of his right hand.  Wheeler has had a history of blisters that have affected his performance and while it's not necessarily a long-term concern, it apparently has become an issue once again to start this season.The blister has prevented Wheeler from throwing his slider and apparently burst during his start last night against Fresno.  He is on pace to make his next scheduled start.  In tow starts, Wheeler has allowed 6 runs (3 earned) in 8.2 innings with 9 strikeouts and 6 walks.